Thailand: SIP providers and connecting a number to the PBX

This page continues the general guide to connecting a provider's number to the PBX, which covers what is the same in every country — the two trunk modes, what to ask the operator, what to enter in the form, network and compatibility and checking the connection. Here you will find the Thai specifics: where to get an 02 number, why calls placed into Thailand from abroad are flagged with a special prefix, and what to ask when local providers publish almost no trunk parameters.

The data was collected on 10 September 2026 from provider websites, the ITU numbering plan and PBX vendors' certification lists; links are in the Sources section.

In brief#

• A dedicated PBX is created for Thai locations. The venue itself needs no permit: the licence issued by the National Broadcasting and Telecommunications Commission (NBTC) is held by whoever sells the service and the numbers. Buying the service from a licensee is enough.
• ⚠️⚠️ The main local trap is the marking of international calls. At the NBTC's direction operators flag incoming calls from abroad: the +698 prefix means a Thai number roaming abroad, +697 means a voice-over-IP call from overseas; subscribers are explicitly advised not to answer such calls, and since 2025 operators must let them be blocked. The conclusion: buy the number from a Thai provider and hand your outbound calls to the same provider, otherwise your venue's calls will reach guests as "+697…" and be rejected en masse.
• Where to start. NT (National Telecom) — the state-owned operator that holds the bulk of the 02 range and is the only provider in the country with publicly known trunk parameters. SIPPER — if the technical side matters: it is the only one that publicly names its codecs (G.711, G.722, G.729, Opus) and compatibility with Asterisk and FreePBX. CallnClear and Call On Cloud — a quick retail start with an open price list.
• Registration is the default mode. Thai providers issue a username and a password, so the «Register with the provider (REGISTER)» checkbox applies. IP authentication appears in the operators' corporate orders (True, UIH) — then your static address has to be added to their allowlist.
• ⚠️ G.729 comes by default. NT's ready-made configuration sets the codecs to "a-law and G.729". Our PBX speaks G.711 and G.722 and has no G.729 — ask for a-law in writing on the order form.
• ⚠️ Almost nobody publishes the server address. With ten of the twelve local providers the host, the port and the mode arrive by e-mail once the contract is signed. Allow a day or two for the correspondence and insist on written parameters before you pay.
• ⚠️ A landline number requires a Thai company. Local operators sign contracts with companies registered in Thailand; for Thai local numbers Twilio states outright that the address "must be within locality or region covered by the phone number's prefix".

Numbers in Thailand#

• The country code is +66, the national prefix inside the country is 0, the international access code is 00.
• A landline number is exactly 8 digits without the leading zero, i.e. "0 + 8 digits" when dialled inside the country. Bangkok and its suburbs (Nonthaburi, Pathum Thani, Samut Prakan) use 2x, plus the newer ranges 10, 16, 18 and 19. Example: +66 2 107 xxxx.
• Provincial codes (the leading digits of the number without the zero):

• Mobile numbers are 9 digits, in the 6x, 8x and 9x ranges.
• ⚠️ Thai VoIP has a range of its own. Non-geographic numbers for voice over IP are 60 and 89, 9 digits long: 0 60x xxx xxx instead of the landline 0 2xxx xxxx. An 02 number offered by a VoIP provider is a resold fixed-line number (usually NT's), not a "VoIP range" one. Guests dial a landline number more willingly, so it matters which range your provider offers.
• The move to 10 digits has been postponed. The 2020 plan promised ten-digit landline numbers from 2025, but a notice dated 8 May 2024 cancelled that: the change will happen only when numbers start running short, with advance notice. As of 2026 a landline number has eight significant digits.
• Special ranges: 1800-xxx-xxx is toll-free for the caller, 1900-xxx-xxx is premium rate, and four-digit service numbers (1xxx) are sold separately. Emergency numbers: police 191, fire 199, ambulance 1669, tourist police 1155.
• In «Lines» enter the number exactly as the provider issued it: the PBX matches the last seven digits, so +66 2…, 662… or 02… makes no difference. For an eight-digit landline number the seven-digit tail is unique within one account, but mobile numbers of different operators can share a tail — do not put numbers that differ only in their first digit into the same account.
• ⚠️ Providers send the incoming number in different formats. Since the 2024 migration NT works with the national format 02xxxxxxx, while the 3CX templates of CallnClear and 2APlus require the main trunk number in the international format (the example in the 2APlus guide is 6622846147). Ask your provider in what form it sends the number on an incoming call.
• Codecs. Ask for G.711 a-law — that is what our PBX accepts.

Who sells a number with a SIP trunk#

NT (National Telecom) — 02 numbers from the holder of the range#

The state-owned operator formed by the merger of CAT Telecom and TOT; it holds almost the entire landline number range and the backbone network. Its SIP trunk service used to be called CAT SIP Connect (the catnextgen.com server); subscribers are now being moved in waves to the NT Nextgen platform: you file a request in the ntnextgen.com portal and NT then e-mails you the new configuration. It is sold as a replacement for an E1/ISDN line, priced by the number of simultaneous channels; the retail entry point for small businesses is the regional NT Metro Service offices.

What to arrange with the provider: order SIP Connect with the required number of channels → obtain numbers or convert an existing NT copper line to SIP → ask for a-law explicitly on the order form, otherwise the operator will leave G.729 → check whether they need our public address (with registration they usually do not) → agree on the caller ID format.

Pitfalls ⚠️

• ⚠️⚠️ Do not change the settings before NT's letter arrives. The move from the CAT platform to NT Nextgen goes in waves on the operator's schedule: both catnextgen.com and res.ntnextgen.com exist, and configuring "for the future platform" produces the classic picture of "registration is up, calls do not go through".
• The old platform still shows up in third-party guides. Before the migration NT worked at catnextgen.com and the username looked like a number with a plus sign (+662107xxxx). Such settings still appear in PBX vendors' manuals — that variant is obsolete.
• NT publishes no Asterisk guide; the manual is downloaded via a link in the subscriber's portal and does not always open from outside Thailand. Ask the manager or an integrator partner for the parameters in writing.

Sources: NT Metro Service — SIP Trunk · the NT Nextgen portal — 10 Sept 2026.

SIPPER — its own VoIP network and publicly stated codecs#

The most informative website on the market. SIPPER claims a dedicated voice network with direct interconnects to NT and True and a Ribbon session border controller at the edge (up to 2,000 simultaneous calls, redundancy, a 99.99 % SLA and a 24/7 network operations centre). It sells numbers in Bangkok and the provinces, mobile numbers for outbound caller ID and packages priced by the number of simultaneous channels.

It is the only provider in the country to publish the technical details: the codecs G.711, G.722, G.729 and Opus, DTMF RFC 2833, T.38 fax, E.164 number formatting and compatibility with "Yeastar, 3CX, Asterisk, FreePBX, Cisco, Avaya, Zoom Phone, Webex". For a third-party PBX the provider explicitly promises to issue SIP credentials, a codec configuration and firewall guidance — that is, registration mode.

What to arrange with the provider: ask for a codec profile of a-law and u-law (plus G.722) without mandatory G.729 → have the encryption requirement lifted for our trunk → route the purchased numbers to the trunk → agree on firewall rules for our «Static IP» and media ports 10000–20000.

Pitfalls ⚠️

• ⚠️ Encryption is their showcase feature, and it does not suit us. TLS and SRTP are presented on the website as an advantage; our PBX does not accept them on trunks. Insist on plain UDP in the very first conversation.
• The advertised quality applies to their own segment. SIPPER's "pure" network runs as far as the interconnects with NT and True, while the leg from our cloud to their controller still crosses the public internet.
• G.729 is on their list and absent from ours. Put the codec set in writing.

Source: SIPPER — SIP Trunk — 10 Sept 2026.

CallnClear — Thai numbers with an open price list#

A Thai provider from the Cal4Care group (Bangkok, Sunphawut Road, +66 2 026 8705). It is on 3CX's list of certified providers for Thailand and claims compatibility with "3CX, Asterisk, Avaya, Cisco, FreePBX and Grandstream". Prices are public: a Thai number costs THB 140 to set up and THB 140 per month; besides Thailand it sells numbers in Australia, India, Japan, Malaysia, New Zealand, the Philippines, Singapore, the USA and Vietnam.

What to arrange with the provider: order a Thai number and the number of simultaneous channels → request G.711 and plain UDP → have the number routed to the trunk → agree on the format of the main trunk number (their guide expects the international format) and on the list of numbers allowed as caller ID.

Pitfalls ⚠️

• ⚠️⚠️ The numbers cannot be ported away. The provider's terms state plainly that its numbers are not transferable at any point in time (except for numbers that were ported in). If you leave, the number is lost — take that into account before printing your signage and business cards.
• There are no public setup guides — the guides section on the new website is still empty, and the parameters arrive by e-mail.
• The group runs many similar brands (CallaCloud, CloudNippon, ConnectViet and others) — make sure the contract is about the Thai platform.

Sources: CallnClear — SIP Trunks · CallnClear — numbers and prices — 10 Sept 2026.

2APlus — a carrier with a 3CX profile and no TLS#

A Thai VoIP carrier operating since 2006, with an office in the CAT Telecom Tower on Charoenkrung Road in Bangkok, phone +662 105 5755. It handles voice termination and DID numbers and serves operators, resellers and call shops; it has been a 3CX partner since 2015 and is on the certified list for Thailand. Its 3CX profile notes: SIP TLS — no, IPv6 — yes, fax — yes, no online sign-up.

What to arrange with the provider: agree on the main trunk number in the international format (66 2 xxx xxxx without the plus sign, as the guide requires) → hand over the list of numbers you may present on outbound calls → request the G.711 codec and the number of channels.

Pitfalls ⚠️

• The focus is wholesale. The carrier works with operators and resellers: a single venue may face a minimum volume or be referred to a partner.
• There are no guides of its own in the open, the only public material being a 3CX forum setup template from 2022; take the parameters from the order form.
• Caller ID must be your own. The guide states that you may present only numbers associated with your account.

Sources: 3CX — 2APlus configuration guide (Thailand) · 3CX — SIP trunk providers in Thailand — 10 Sept 2026.

Call On Cloud — an NT number delivered as a trunk#

A cloud PBX provider from Bangkok (02-028-7722) that sells "a number in the form of a SIP trunk": it takes an 02 landline number straight from NT and delivers it to the customer over the internet, promising compatibility with the customer's own PBX. Its price list is the most transparent on the market: THB 1,200 per year for a number, THB 960 per year for one simultaneous channel, THB 0.80 per minute to mobiles and other zones and THB 3 per call inside its own zone. "Golden" numbers are sold separately, from THB 5,000 for the Gold tier to THB 100,000 for the top one.

What to arrange with the provider: order the required number of simultaneous channels — that is the capacity of the trunk → have the number routed to our trunk → request G.711 and plain UDP.

Pitfalls ⚠️

• Their main product is their own cloud PBX. A trunk to someone else's PBX is on sale, but you have to spell that out to the manager.
• Inside their own zone the charge is per call, not per minute. For a venue with short calls that can work out more expensive than per-minute billing: do the maths in advance.

Source: Call On Cloud — numbers — 10 Sept 2026.

More providers: parameters only under contract#

These companies do have (or claim) a trunk for your own PBX, but the server address, the port and the mode are issued by a manager once the contract is signed. There is no "what to enter" table here: fill the form in from the sheet you receive, and take your questions from «What to ask the provider».

• True Corporation (TrueBusiness) — the Internet SIP Trunk product runs over the public internet, with no dedicated circuit, and is claimed to be compatible with Cisco, Avaya, Yeastar, 3CX and contact-centre platforms; four-digit short numbers and toll-free 1800 numbers are supported and the channel count is changed on request. Order it through the 1239 call centre or the web form. ⚠️ The service description mentions encryption: if the trunk turns out to be offered only in encrypted form, the setup will not work — our PBX accepts UDP and TCP. ⚠️ True will push its own cloud PBX — ask for a trunk to your own PBX explicitly.
• UIH (United Information Highway) — a corporate operator that sells "SIP Trunk / IP Phone / Cloud PBX" as a managed service together with its own access circuit. ⚠️ Our scenario (a PBX in the cloud, outside the UIH network) is unusual for a managed service — check before paying that they will hand the trunk out to the internet.
• AIS Business — the country's largest mobile operator. ⚠️ It has no public "SIP trunk for your PBX" page; third-party providers list AIS among their direct interconnects, so the capacity is sold through a manager. Put it plainly in your enquiry: "SIP trunk to customer-owned IP PBX (Asterisk)".
• dtac Business — its voice line-up contains only its own cloud PBX, with no trunk to a third-party PBX on public offer. For a trunk go to TrueBusiness.
• SMART Life Tech (VoIP Thailand) — a 3CX partner and reseller from Bangkok, interesting for its numbers in different cities: 02 Bangkok, 076 Phuket, 052 Chiang Mai, Hua Hin and Pattaya — which matters for a venue, as the guest sees a local code. ⚠️ It is a reseller: the capacity and the numbers belong to others (NT or True), so an incident is diagnosed through two parties.
• 1-TO-ALL — a Thai internet provider and business VoIP operator with direct interconnects to local operators and a 99.9 % voice SLA. ⚠️ The SLA applies inside its own network and not to the "our cloud → Thailand" leg; the company actively sells its own cloud, so ask for a trunk explicitly.
• Protollcall — a cloud PBX and contact centre from Bangkok that sells both numbers and equipment for a PBX on the customer's premises. ⚠️ It is not publicly stated whether a number is sold as a trunk separately from their cloud: make that your first question.

International providers with Thai numbers#

You can also buy a Thai number from a global provider — their trunk parameters are described in the provider catalogue in the admin panel and in the general guide.

• Twilio — the only provider in 3CX's "Preferred" category for Thailand. The document requirements are split: for local numbers the address must be within the locality or region covered by the number's prefix and the document is a Thai government-issued ID card or a Thai company registration extract; for toll-free and mobile numbers the address may be anywhere in the world.
• DIDWW — Thai local numbers in three zones: +66 (2) Bangkok, +66 (52) Chiang Mai and +66 (33) Chonburi, plus national, mobile and toll-free numbers. In all zones inbound calls, SIP trunking and inbound fax are supported, while inbound and outbound SMS and number portability are not.
• Telnyx — Thai numbers "starting at $10 per month" routed through tier-1 in-country carriers; its requirements tool shows the paperwork when you order.
• AstraQom Thailand — an international carrier with a dedicated storefront for Thai trunks and numbers; it promises free engineering help with Asterisk, FreePBX and 3CX setups. Parameters are issued after the order.
• ⚠️⚠️ The general caveat about +697. The marking hits the scenario in which a call enters Thailand from abroad. For inbound calls to a Thai number it does not matter; for outbound calls with a Thai caller ID it is critical. It makes sense to use an international provider for receiving calls and to hand outbound calls to a Thai licensee; when ordering, ask directly where the outbound traffic is terminated.

Porting a number#

• Mobile numbers can be ported. Porting between AIS, dtac, True and NT has worked since 2011 and since 2017 runs paperlessly: a short-code request *151* with your ID number, activated in about a day.
• ⚠️ Landline numbers apparently cannot be ported. There is no open information about portability of fixed numbers, and DIDWW marks portability as unsupported for every Thai local number. In practice this means the landline number belongs to the operator: changing provider means changing the number, so the choice is made for years.
• Inside NT a service migration is possible: a copper line with an existing number is converted to SIP Connect. That is not porting to another operator but a change of service with the same one.
• Plan the switch with an overlap: keep the old number and forward its calls to the new one while your signage, business cards and directory listings are updated.

Rules and paperwork#

If it does not work#

1. The NT trunk has registered but calls do not go through. The most common reason is configuring the new platform before the operator's letter arrives: the move from CAT to NT Nextgen goes in waves, and until your wave the old address is the working one. The second option is that NT uses different addresses for registration and for calls: ask which one belongs in the "SIP host" field.
2. The call connects but there is silence in one or both directions. Codecs. NT's ready-made configuration offers a-law and G.729, SIPPER's list also includes G.729, and some providers do not name their codecs at all. You need G.711 a-law/u-law or G.722 — enabled on the provider's side.
3. The provider offers an encrypted trunk only. Our PBX does not accept TLS or SRTP on trunks — ask for plain UDP. 2APlus has no encryption at all, while SIPPER, CallnClear and True treat it as optional.
4. Registration is green but no calls arrive. Check that the purchased number is routed to this very trunk and that the "Accepts calls" checkbox on the line is still ticked. If you untick it for every number of a trunk, the PBX drops the registration and no inbound calls arrive at all.
5. Calls land on the wrong line. Compare the last seven digits of your numbers and ask the provider in what form it sends the number: NT uses the national 02xxxxxxx, while the CallnClear and 2APlus guides require the international format.
6. Outbound calls are rejected. Usually it is the caller ID: only the numbers on your contract may be presented. Leave «Show as» empty. On a corporate trunk (True, UIH) check whether our «Static IP» is on their allowlist.
7. Guests say your number shows up as "+697…" and they do not pick up. That means your outbound calls are terminated into Thailand from abroad. Move outbound traffic to a Thai licensee — the marking is applied precisely to the international leg.

Causes that do not depend on the country are in «If calls do not go through».

Frequently asked questions#

Which provider should I start with?#

With NT if you need a genuine 02 landline number from the holder of the range and are ready for a contract with the state-owned operator: it is the only provider in the country whose trunk parameters are publicly known. For a quick retail start take CallnClear or Call On Cloud: both have open price lists, the numbers are the same (Call On Cloud takes 02 straight from NT), and connection takes days rather than weeks. A large site with quality requirements is best served by SIPPER: its own network, publicly stated codecs and declared compatibility with Asterisk and FreePBX.

What is the +697 prefix and how does it affect me?#

It is the regulator's marking: +697 means "voice over IP from overseas" and +698 means a Thai number roaming abroad. Subscribers are advised not to answer such calls, and operators must give them the ability to block them. For guests calling your Thai number it makes no difference. The dangerous case is the reverse one: if your PBX's outbound calls enter the Thai network from abroad, the guest sees "+697…" and will most likely not answer. So hand outbound calls to a Thai provider and ask, when ordering, where the call is physically terminated.

Do I need a Thai company?#

For an 02 landline number — in practice yes: local operators sign the contract with a company registered in Thailand, and the address must belong to the number's zone. International providers are more lenient about mobile and toll-free numbers, whose address may be anywhere in the world, but for a local number they will still ask for Thai paperwork.

Why does everyone mention G.711 while my provider offers G.729?#

G.729 compresses voice harder and saves bandwidth, so Thai operators put it in the default profile — NT's ready-made configuration lists a-law and G.729. Our PBX speaks G.711 (a-law and u-law) and G.722 and has no G.729: if the provider leaves only that, the trunk will register but there will be no audio. Ask for a-law in writing on the order form.

What should I ask the provider first?#

Four things, because Thai providers hardly publish any of them: the server address and port; whether G.711 a-law is available; registration or IP authentication (and in the latter case, whether the provider accepts a foreign static address); and in what form the number arrives on an incoming call. After that — the number of simultaneous channels and the procedure for confirming caller ID. The full list is in «What to ask the provider».

Will I keep the number if I change provider?#

A mobile one, yes — porting works. A landline one, most likely not: there is no information about porting fixed numbers between Thai operators, and some providers state outright that their numbers are not transferable. Choose a provider with years in mind and do not print the number on expensive materials in the first month.

Sources#

All links checked on 10 September 2026.

Regulator and numbering

• ITU Operational Bulletin — Thailand numbering plan, country code +66 (PDF): https://www.itu.int/dms_pub/itu-t/oth/02/02/T02020000CD0004PDFE.pdf
• NBTC — the regulator's website: https://www.nbtc.go.th
• The Nation — the NBTC's warning about the +697 and +698 prefixes: https://www.nationthailand.com/thailand/general/40021975
• Bangkok Post — the NBTC's eight anti-fraud measures: https://www.bangkokpost.com/business/general/3061744/nbtc-endorses-8-cybercrime-measures
• The Nation — new rules on SIM cards, SMS and foreign calls: https://www.nationthailand.com/blogs/news/policy/40054768

Providers

• NT Metro Service — SIP Trunk: https://nt-metro-service.com/en/product-and-service/communication/sip-trunk/
• NT Nextgen — subscriber portal: https://ntnextgen.com/login
• TrueBusiness — Internet SIP Trunk: https://business.true.th/en/solutions/internet-sip-trunk
• dtac Business — Cloud PBX: https://business.dtac.co.th/en/products/cloud-pbx
• AIS Business: https://www.ais.th/en/business
• UIH — SIP Trunk / IP Phone / Cloud PBX: https://www.uih.co.th/th/products-services/managed-services-th/sop-trunk-ip-phone-cloud-pbx/
• SIPPER — SIP Trunk: https://www.sipper.co.th/th/sip-trunk
• CallnClear — SIP Trunks: https://www.callnclear.com/sip-trunks
• CallnClear — numbers and prices: https://www.callnclear.com/did-numbers
• 3CX — 2APlus configuration guide (Thailand): https://www.3cx.com/community/threads/2aplus-sip-trunk-configuration-guide-thailand.79894/
• 3CX — certified SIP trunk providers in Thailand: https://www.3cx.com/partners/sip-trunks/thailand/
• Call On Cloud — numbers: https://www.calloncloud.io/service/did-number
• SMART Life Tech — SIP Trunk Thailand: https://www.smartlifetech.co.th/blogs/post/SIP-Trunk-Thailand-VoIP-Thailand
• 1-TO-ALL — Business VoIP: https://www.1-to-all.com/business-voip
• Protollcall: https://protollcall.com/
• AstraQom — Thailand SIP Trunks: https://www.astraqom.com/th/thailand-sip-trunks/

International numbers and compatibility

• Twilio — regulatory guidelines for Thailand: https://www.twilio.com/en-us/guidelines/th/regulatory
• DIDWW — Thailand local numbers: https://www.didww.com/phone-numbers/local-numbers/Thailand/Local
• Telnyx — Thailand phone numbers: https://telnyx.com/phone-numbers/thailand

Related pages#

• Connecting a provider's number to the PBX — the common steps, trunk modes, network and connection check.
• Setting up SIP phones — how to connect desk phones and DECT handsets to extensions.