Vietnam: 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 everything that is the same in any country — the two trunk modes, what to ask the operator, what to enter in the form, network and compatibility and the connectivity check. Here we cover what is specific to Vietnam: why this country almost always uses IP authorisation, who to buy a number from, and the three traps waiting for you on the very first test call.

The data was collected on 10 September 2026 from operator websites, regulator documents and the connection sheets published by Vietnamese integrators; links are in the "Sources" section.

In brief#

• A dedicated PBX is created for Vietnamese locations. The licence is held by the Vietnamese operator you buy the number and the trunk from; a contract with that operator is all your venue needs.
• ⚠️⚠️ The country's main peculiarity: a local trunk almost always works by IP address, not by login and password. In every published instruction the trunk is set up as a "Peer Trunk": the operator sends calls to your PBX's static address and accepts calls from it, with no username and no password. This is the IP-auth (no registration) mode — the checkbox in the trunk form stays cleared. A dedicated PBX does have a static address; you need to hand it to the operator.
• Where to start: VNPT — the only operator in the country whose connection sheet is published in full, codecs included (it does have G.711 a-law/u-law and G.722); FPT Telecom — the country's first SIP trunk provider, promising provisioning in 1–5 days; ConnectViet — the only Vietnamese provider that works in registration mode and sells numbers online, the fastest route when there is no time to wait for a corporate contract.
• ⚠️ Three traps that leave the trunk down or silent: Viettel uses port 55000, not 5060; with VNPT the audio arrives from different addresses than the signalling (signalling from one IP, RTP from two others), so a firewall opened for one address only produces a call with no sound; and ConnectViet may deliver the trunk username instead of the number in incoming calls, which breaks the "this number → this scenario" rule.
• ⚠️ A foreign company will not be given a local number. The contract is signed by a Vietnamese legal entity: a business registration certificate (giấy phép kinh doanh) and the representative's ID are required. Twilio asks for exactly the same for Vietnamese numbers — a business registration or an investment licence and an address in the country; a PO box is not accepted.
• ⚠️ Register a caller name (voice brandname) before your first outbound campaign. Without a registered caller identifier, a business call to a customer qualifies as a spam call; the venue registers it through its own operator and the name is valid for three years.

Numbers in the country#

• Country code — +84, the national prefix inside the country is 0.
• Landline numbers: 0 + area code + subscriber number. The area code has two digits in Hanoi (24) and Ho Chi Minh City (28) and three digits in the provinces (Da Nang — 236). The subscriber part is 7 or 8 digits, so the national form is 10–11 digits with the leading zero, and the international form is +84 plus 9–10 digits.
• Mobile numbers: 03x, 05x, 07x, 08x, 09x plus 7 digits — nine digits without the leading zero (+84 9xx xxx xxx).
• Internet telephony numbers live inside the landline areas, each operator having its own subscriber series: FPT — 73… (028 73xx xxxx), CMC Telecom — 710 (028 710 xxxxx), iTel — 777 (024 777 xxxxx), SPT — 55…. Vietnamese customers recognise these as "a tech company's number" — fine for a venue, but it reads as less established than an ordinary landline.
• Service numbers: 1900 plus 4 or 6 digits (premium rate for the caller) and 1800 plus 4 or 6 digits (toll-free). ⚠️ Both are inbound only: under the applicable circular, premium-rate numbers are used solely to receive incoming calls and may not be used to call out, so you cannot put 1900/1800 into Display as.
• Emergency services are three-digit: 112 (rescue), 113 (police), 114 (fire), 115 (ambulance).
• In Lines enter the number exactly as the operator issued it: the PBX matches the last seven digits, so writing it with +84, with 0 or with 0084 makes no difference. VNPT's connection sheet lists the accepted forms explicitly: 0X, +84X, 0084X. Other operators do not publish the format — ask when you connect.
• ⚠️ The last-seven-digits trap. With the eight-digit subscriber numbers of Hanoi and Ho Chi Minh City the match drops the first digit: 028 7300 1234 and 028 3300 1234 both end in 3001234. Do not put numbers that differ only in that digit into one account.
• Codecs. Ask for G.711 a-law/u-law — that is what our PBX accepts. Codecs are publicly confirmed for VNPT only; the other operators do not publish the list, so request it in writing before signing.

Who provides a number with a SIP trunk#

VNPT / VinaPhone — the only one with a published parameter sheet#

The state telecom group; its "Trung kế SIP Trunking" has been sold since 2014 in two flavours: a trunk on a landline number (including 1800 and 1900) and a trunk on a mobile number, both over fibre, a leased line or ordinary internet. Prices on the sales portal as of 10.09.2026: 250,000 ₫ one-off connection, a monthly fee of 30,000 ₫ for a landline number and 49,000 ₫ for a mobile one, 220 ₫ per domestic minute; the number of simultaneous calls equals the number of channels you pay for.

This is the only operator in the country whose connection sheet is published in full, codecs included: it does offer G.711 a-law, G.711 u-law and G.722, so the overlap with our PBX is guaranteed. VNPT also runs a separate IMS platform — the same number, but in registration mode, with the address ims.vnpt.vn and a regional outbound proxy; which of the two you have been sold is stated in your connection sheet.

What to enter in the admin panel (Telephony → "Trunks and connections" → Add provider):

What to set up on the provider's side: sign a "Trung kế SIP" contract of the right kind (landline or mobile) → hand over Static IP from the "Server" tab as the delivery address and as an allowed address for outbound calls → agree the number of channels → obtain the connection sheet with the signalling addresses and the addresses the audio comes from → point the purchased numbers at the trunk → set your number as the outbound caller ID.

Traps ⚠️

• ⚠️⚠️ The audio does not come from the signalling address. In the connection sheet, signalling comes from one address while RTP comes from two neighbouring ones (14.238.2.147 and 14.238.2.148). If traffic is restricted to the signalling address only, the call will connect with no sound. Confirm both media addresses when you connect.
• The addresses are regional. VNPT runs provincial nodes: the connection sheet of a neighbouring city will not fit you, and that applies both to the ordinary trunk and to the outbound proxy of the IMS variant.
• Your own port can be changed. On request the operator moves the trunk from 5060 to an arbitrary port — that same port then goes into the trunk form.

Sources: VNPT — SIP Trunking, description and prices · VNPT connection sheet — 10.09.2026.

FPT Telecom — the country's first trunk and fast provisioning#

The pioneer of SIP trunking in Vietnam: the service has been running since 2008 on the operator's own network with the landline series 73…. The business range covers Hosted PBX, IP Centrex, SIP Acc, SIP Trunk and DID/DOD, plus 1800 6XXX and 1900 636XXX hotlines; the operator promises provisioning in 1–5 days, which is fast by Vietnamese standards.

FPT publishes no technical pages of its own: the trunk parameters come from three independent integrators, and they agree with each other.

What to enter in the admin panel

What to set up on the provider's side: a SIP Trunk contract (or SIP Acc, if you want the username-and-password variant) → hand over the PBX's "Static IP" for the allowed addresses → agree the number of channels and the 73… landline numbers → confirm the number format in incoming calls and the addresses the audio comes from.

Traps ⚠️

• ⚠️ FPT has two similar products. "SIP Trunk" works by address, "SIP Acc" uses a username and a password; which one you were sold is only visible in the contract, and the registration checkbox depends on it.
• ⚠️ The backup address is a second address, not a second trunk. Our PBX recognises the provider by the trunk's SIP host, so a call arriving from the backup address may not be recognised. Ask FPT for both addresses and create a second trunk for the backup one.
• The operator publishes no parameters — every figure here is second-hand, so always check it against your connection sheet.

Sources: FPT VoIP — SIP Trunk and DID/DOD · ODS — configuring Vietnamese operators' SIP trunks — 10.09.2026.

Viettel Telecom — the largest network and port 55000#

The country's largest operator, offering SIP trunking since 2018 on both landline and mobile numbers ("Mobile SIP" — a mobile number used as the venue's hotline), over the internet or a leased line. For delivery, couriers and a small outlet a mobile hotline is often handier than a landline: it is instantly recognisable and moves with the business inside the country.

What to enter in the admin panel

What to set up on the provider's side: a contract through a Viettel corporate manager → hand over the PBX's "Static IP" → agree the number of channels and the numbers → request a connection sheet with the port and the signalling and audio addresses → confirm in writing that the trunk is delivered with G.711.

Traps ⚠️

• ⚠️⚠️ Port 55000 is not a typo. An instruction copied from a neighbour with port 5060 leaves the trunk silent. That said, 55000 is not guaranteed either: some sites get their own port, and it is always stated in the contract.
• Your own port is negotiable too. On request the operator moves the connection from 5060 to an arbitrary port — which then goes into the trunk form.
• A mobile number stays mobile. "Mobile SIP" is convenient, but such a number will not turn into a landline and does not move to another network together with the trunk service.

Sources: Viettel — SIP Trunking for business · Viettel connection sheet — 10.09.2026.

Indochina Telecom (iTel) — 777-series numbers with no channel limit#

A virtual operator with the mobile prefix 087 and the landline series 777 on its own VoIP platform — numbers such as 024 777 99999. The "SIP Trunking cố định" product is simple: no limit on simultaneous calls, no limit on the number of numbers across the country, 220,000 ₫ per month to keep a number, and a single registered number shown to the outside world.

What to enter in the admin panel

What to set up on the provider's side: order a 777-series number → hand over the PBX's "Static IP" → agree the number of channels → set your number as the outbound caller ID → request confirmation of G.711 and of the number format in incoming calls.

Traps ⚠️

• This is a virtual operator on someone else's infrastructure. Check route quality and the terms for restoring service before moving the venue's main number to iTel.
• The 777 series is recognisable as a VoIP number — some Vietnamese subscribers will not call such numbers back.
• Only one number is shown outbound. If different outlets need to display different numbers, that is a separate conversation with the operator.

Sources: Indochina Telecom — SIP Trunking cố định · Buss Call — operators' parameters and the connection procedure — 10.09.2026.

ConnectViet — registration mode and ordering a number online#

The Vietnamese arm of the Singaporean Cal4Care group (office in Ho Chi Minh City). For us it is the exception to the Vietnamese rule: the only local provider that works in registration mode, with an online portal, self-service ordering and a number activated right after purchase. It claims certification with 3CX, Asterisk, FreePBX, Avaya, Cisco and Grandstream; it has no encrypted (TLS) trunk, which suits us fine. Call records are kept in the portal for 90 days. If there is no time to wait for a corporate contract, or the customer is foreign, start here.

What to enter in the admin panel

What to set up on the provider's side: create the trunk and the number in the portal → receive the parameters by email → point the number at the trunk → ask what arrives in the call: the number or the trunk username → agree G.711 → clarify the contract term.

Traps ⚠️

• ⚠️⚠️ Incoming calls may carry the trunk username instead of the number. In the provider's own FreePBX instruction the inbound route is created on the username. If that still holds, matching a line by number will not work: the call is accepted, but all numbers merge into one line. With a single number it does not matter; with several, ask how to enable number delivery.
• There are no public instructions. The provider's former guide pages return a 404 — current parameters come from support only.
• The contract may be long. A sister company in the group signs for 24 months; confirm the Vietnamese terms before you pay.

Sources: ConnectViet — SIP Trunks · ConnectViet — FAQ · 3CX — certified providers in Vietnam — 10.09.2026.

More providers: parameters issued by a sales manager#

These companies do offer a trunk to your own PBX, but the server address, the port and the number format are sent after the contract is signed. There is no "what to enter" table here: fill in the form from the sheet you receive, and take your questions from What to ask the provider.

• CMC Telecom — SIP trunking since 2013, strong in the corporate and data-centre segments; its signature resource is the premium landline hotline series 710 (028 710 xxxxx). ⚠️ CMC is keen to sell "a number plus our own cloud PBX": state explicitly in your request that you need a SIP trunk to your own IP PBX, otherwise you will be offered their PBX with no outside trunk.
• SPT (Saigon Postel) — the oldest alternative operator in Ho Chi Minh City; its service description is the closest to our scenario: a trunk "from the customer's equipment" to the operator's system over ordinary landline numbers or 1800/1900. Its landline series is 55…. ⚠️ Presence is mostly in Ho Chi Minh City and the south: for a venue in Hanoi look at VNPT or FPT.
• MobiFone — a SIP 2.0 trunk on a MobiFone mobile hotline number only; the service has no landline numbers. ⚠️ To a guest this looks like "a call from a mobile", not "a call from a restaurant". The service is also pitched together with the operator's own cloud contact centre — insist on a plain trunk.
• VOIP24H / Buss Call — not an operator but an integrator: it connects the trunk of any operator in the country (FPT, VNPT, Viettel, CMC, SPT, iTel) to your PBX, Asterisk included. Its materials are the fullest public summary of operator parameters, and it describes our case verbatim: if the PBX has its own static address and sits in a data centre, the trunk is declared directly through that address. ⚠️ A middleman adds its own margin and its own timescales: in a dispute there is now a third party between you and the operator.
• OMICall (VIHAT) — one of the three largest Vietnamese cloud PBX providers; the interesting part is Mobile SIP Trunk: a Viettel, MobiFone or VinaPhone mobile number used as the PBX number, connected to the customer's own system. ⚠️ The product is built around their own cloud and no parameters are published at all — before signing, check that the trunk is delivered over plain UDP and with G.711.
• StringeeX — a large local cloud PBX and calling API; no trunk to an external PBX is advertised. It suits you if you are willing to give up your own PBX rather than connect a number to it.

International providers with Vietnamese numbers#

Cards for the popular international providers are already in the catalogue when you add a provider — the server address and the mode fill in automatically. The Vietnamese specifics:

• DIDWW — Vietnamese landline and toll-free numbers are available and, per the provider's own data, no owner registration is required for them: this is the simplest way for a foreign company to get a Vietnamese number. ⚠️ Inbound only, though: DIDWW has no domestic outbound termination in Vietnam, and its service page marks local trunking as unavailable. You will not be able to call out with a Vietnamese caller ID through it.
• Twilio — sells Vietnamese numbers, but the requirements are strict: landline and mobile numbers need a Vietnamese business registration or an investment licence, the representative's ID and an address in the number's area (a PO box is not accepted). A toll-free number, conversely, requires an address outside the country.
• Telxi — listed among 3CX's certified providers for Vietnam and publishes its trunk parameters (registration, plain UDP). Whether it actually holds Vietnamese numbers is not publicly confirmed — ask in writing before paying.
• Tata Communications — on the same list, but it is a wholesaler: it works under contract, and number availability and parameters are confirmed through sales.
• ⚠️ Common caveats for all international providers. Emergency numbers 112/113/114/115 cannot be dialled through such a number. And calling a Vietnamese subscriber with a spoofed Vietnamese caller ID over a foreign route leads straight into the spam-call rules and into being blocked by local operators.

Number porting#

• Only mobile numbers are portable. Portability has worked since 2018 through the national porting centre, for both prepaid and postpaid; the request goes to the receiving operator, and the grounds for refusal are now limited by regulation — the operator cannot invent its own.
• ⚠️⚠️ Landline and VoIP numbers are not portable between operators. The series 73… belongs to FPT, 710 to CMC, 777 to iTel and 55… to SPT: leaving an operator means changing the number, and with it the signage, business cards, directory listings and the sticker on the till.
• A practical rule for a venue: put on the signage the number of the operator you are prepared to stay with for years, and run experiments on a second number. Plan any move with a period of parallel operation: keep the old number and forward it to the new one.
• 1800 and 1900 are the operator's resource and leave together with it.
• Register the number to the company, not to an employee. The contract and the caller name are tied to the legal entity; a number registered to a contractor leaves with them.

Rules and paperwork#

If it does not work#

1. "Check connection" fails with Viettel. Check the port first: this operator uses 55000, not 5060. The second candidate is the address: operators' addresses are regional, and figures from somebody else's instruction may not match your site.
2. The call connects but there is silence one way or both. Two local explanations. First, the audio arrives from addresses other than the signalling address (that is how VNPT works) and those were never allowed. Second, codecs: G.711 is publicly confirmed for VNPT only, other operators have to be asked in writing, and our PBX needs G.711 or G.722.
3. The operator says the trunk is live, but no calls come in. In IP mode the operator sends calls to the address you gave it: make sure that was the "Static IP" from the "Server" tab and not the venue's office address. Also check the "Accepts calls" toggle on the line: if you clear it on every number of a trunk, the PBX stops recognising the provider.
4. Incoming calls land on the wrong line. Either the provider sends the trunk username instead of the number (as ConnectViet does), or the last seven digits of two eight-digit Hanoi or Ho Chi Minh City numbers coincide — see "Numbers in the country".
5. Outbound calls are rejected. It is nearly always the caller ID: Vietnamese operators only let through the numbers on your contract, and they do not let 1800/1900 out at all. Leave Display as empty.
6. You were sold the wrong thing. Large operators and cloud PBX vendors are eager to sell a "tổng đài ảo" — their own cloud PBX with extensions instead of a trunk. Name the trunk to your own PBX explicitly in your request.

Causes that are the same in any country are in If calls do not go through.

Frequently asked questions#

Which provider should I start with?#

With VNPT if you want predictability: it is the only operator in the country with a fully published connection sheet naming both the codecs (G.711 a-law/u-law and G.722 are there) and the accepted number formats. FPT Telecom wins on speed — 1–5 days to provision — and ConnectViet on the fact that it works in registration mode and sells numbers online, with no corporate contract to wait for.

Why are there almost no username-and-password trunks in Vietnam?#

That is how the market developed: every published instruction from a local operator describes the trunk as a link between two hosts by address ("Peer Trunk"), with no account. This suits us — a dedicated PBX has a static address, and that is what you give the operator. Among local providers only ConnectViet offers registration mode, while VNPT runs a separate IMS platform where registration is done with the number.

Do I need a Vietnamese company?#

For a local number — effectively yes: the contract with an operator is signed by a legal entity, and a business registration certificate plus the representative's ID are required. Twilio asks for the same documents for Vietnamese numbers, plus an address in the country. A foreign company can get an inbound Vietnamese number from an international provider — DIDWW, for example, where no owner registration is required for Vietnamese numbers.

Can I use a 1900 or 1800 number for outbound calls?#

No. Under the applicable circular, premium-rate and toll-free numbers are used solely to receive incoming calls and may not be used to call out. Put an ordinary landline or mobile number from your contract into Display as, or leave the field empty.

What should I ask the operator first?#

Five things: the signalling address and the port; which addresses the audio comes from (with VNPT they differ from the signalling address); whether G.711 a-law/u-law is available; the number format in incoming calls; and how many channels the tariff includes. The full list is in What to ask the provider.

Will I keep the number if I change operator?#

The landline one — no: only mobile numbers are portable in Vietnam, while landline and VoIP series belong to a particular operator. Plan any move with a period of parallel operation: keep the old number and forward calls to the new one while the signage, business cards and directory listings are updated.

Sources#

All links checked on 10.09.2026.

Regulator and numbering

• Decree 163/2024/NĐ-CP — implementing the 2023 Telecommunications Law: https://vanban.chinhphu.vn/?pageid=27160&docid=212144
• Circular 27/2021/TT-BTTTT — amendments to the numbering plan: https://vanban.chinhphu.vn/default.aspx?pageid=27160&docid=205070
• Ministry of Science and Technology — mobile number porting procedure and technology: https://mst.gov.vn/thu-tuc-va-ki-thuat-chuyen-mang-giu-so-can-nghien-cuu-ki-197100252.htm

Providers

• VNPT — SIP Trunking, description and prices: https://banhangvnpt.vn/dich-vu/dich-vu-sip-trunking-2-57
• FPT Telecom — FPT VoIP (SIP Trunk, DID/DOD): https://fpt.vn/en/business/services/fpt-voip.html
• Viettel — SIP Trunking for business: https://giaiphapviettel.vn/dich-vu/37/sip-trunking--trung-ke-sip-%E2%80%93-dich-vu-thoai-tren-nen-voip-cho-doanh-nghiep.html
• MobiFone — Dịch vụ Tổng đài SIP Trunk: https://solutions.mobifone.vn/vi/dich-vu-tong-dai-sip-trunk
• CMC Telecom — 710-series hotline numbers: http://tongdaiao.cmctelecom.vn/choose-hotline/
• SPT — Dịch vụ SIP Trunk: https://telecom.spt.vn/data/dich-vu-sip-trunk.html
• Indochina Telecom (iTel) — SIP Trunking cố định: https://indochinatelecom.vn/sip-trunking-co-dinh/
• ConnectViet — SIP Trunks: https://www.connectviet.com/sip-trunks/
• VOIP24H — SIP trunking and connecting to an IP PBX: https://voip24h.vn/dich-vu-sip-trunking/
• OMICall — Mobile SIP Trunking: https://omicall.com/mobile-sip-trunking/

Connection parameters and international numbers

• Trường Thịnh Telecom — VNPT connection sheet: https://truongthinhtelecom.com/cau-hinh-siptrunk-vnpt/
• Trường Thịnh Telecom — Viettel connection sheet: https://truongthinhtelecom.com/cau-hinh-siptrunk-viettel/
• Buss Call — connection procedure and operator parameters: https://www.busscall.vn/huong-dan-dang-ky-so-sip-trunk/
• ODS — configuring Vietnamese operators' SIP trunks: https://www.ods.vn/tin-cong-nghe/cau-hinh-sip-trunk.html
• 3CX — certified SIP providers in Vietnam: https://www.3cx.com/partners/sip-trunks/vietnam/
• Twilio — regulatory guidelines for Vietnam: https://www.twilio.com/en-us/guidelines/vn/regulatory
• DIDWW — SIP Trunking in Vietnam: https://www.didww.com/voice/global-sip-trunking/Vietnam

Related pages#

• Connecting a provider's number to the PBX — the general steps, trunk modes, network and the connectivity check.
• Setting up SIP phones — connecting desk phones and DECT handsets to extensions.