Hong Kong: 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 Hong Kong: why the trunks of the big operators usually cannot reach a cloud PBX, who to buy a number from instead, and how a landline number differs from a 58-series VoIP number.

The data was collected on 10 September 2026 from provider websites, the 3CX list of certified providers and documents of the regulator OFCA; links are in the "Sources" section.

In brief#

• A dedicated PBX is created for Hong Kong locations. Hong Kong is a jurisdiction separate from mainland China, with its own regulator (OFCA) and its own licences; mainland restrictions do not apply to it. The venue needs no licence of its own — it is held by the provider you buy the number from.
• ⚠️⚠️ The main divide is "operator over its own line" versus "provider over the internet". HKBN and the "local" variant of the HKT trunk arrive at a PBX in the office over the operator's cable and into its private network — such a trunk cannot be connected to a cloud PBX. HGC and ComNet sell the trunk together with their own access, and a trunk "into someone else's cloud" has to be requested explicitly.
• Where to start: 58VOIP — the only one with a published registrar address for customers in Hong Kong (siphk.58voip.com); the mode is registration over UDP, exactly what our PBX supports; 28VOIP / Matrix — a local provider with the same mode, parameters sent by email. HKT — if you specifically need a 2/3 landline number: it has an internet trunk with registration, but before ordering find out whether it can work without media encryption (SRTP).
• ⚠️ A landline number or a 58 number. Numbers of the 2 and 3 series are full fixed-line service (Class 1) and can be ported. 58-series VoIP numbers (Class 2) are sold by almost every internet and international provider: they are cheaper and faster to get, but cannot be ported — change provider, and the number on your sign changes too.
• ⚠️ All numbers have eight digits, while the PBX matches a line by the last seven. To the PBX 2345 6789 and 3345 6789 are the same — do not put two numbers that differ only in the first digit into one account.
• Paperwork depends on the seller: international providers sell national numbers to businesses only (company registration, proof of address), but a local address is not required.

Numbers in the country#

• The country code is +852. There is no national prefix (like "0"): inside Hong Kong you dial exactly 8 digits, and in international format it is 852 plus the same 8 digits (+852 2123 4567).
• The first digit defines the category (OFCA numbering plan, issue 1.9.2026):

• In "Lines" enter the number the way the provider issued it: the PBX matches the last seven digits, so writing it with or without +852 makes no difference.
• ⚠️ The seven-digit trap. A Hong Kong number has 8 digits, but only the last 7 are matched: 2345 6789 and 3345 6789 share the same tail and merge into one line. If the venue has two numbers (for example, a landline and a 58 number), check this when you add the second line.
• The format of the number in an incoming call depends on the provider: HKT and 58VOIP send the national format (8 digits), Tata Communications and international providers send the international one (852…), 28VOIP, per its 3CX listing, sends a short number like 4621, and HKBN sends the last three digits of the range. In the last two cases the line cannot be told apart by number, and the call goes to the trunk's general route.
• ⚠️ The emergency number 999 has three digits, and outbound dialling that short does not go out through a trunk. Keep a mobile phone at hand for calling 999.
• Codecs. A codec is publicly confirmed only for HKT (G.711 u-law). With everyone else ask for G.711 a-law/u-law — that is what our PBX accepts; "G.729 only" will not work.

Who provides a number with a SIP trunk#

58VOIP — a public registrar for Hong Kong#

A provider of SIP trunks and numbers for Hong Kong and mainland China (Shenzhen, Guangzhou, Shanghai), certified by 3CX as a supported provider for Hong Kong. It is in its 3CX listing that the address is published: "If you located in Hong Kong you need to use "siphk.58voip.com" as your registrar address". The same listing says encrypted SIP (TLS) is not supported — a plus for us, it is an ordinary UDP trunk; there is no self-service portal, orders go through sales.

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

What to set up with the provider: order a trunk with the number of channels you need and a Hong Kong number → check whether the login matches the trunk number and in what format the number arrives in incoming calls (per the 3CX listing — national format) → get the list of numbers allowed as outbound caller ID → agree on G.711 codecs. The full list of questions is in "What to ask the provider".

Pitfalls ⚠️

• Codecs are not published. Before paying, get written confirmation that G.711 (a-law or u-law) is available and G.729 is not required.
• The port is not given in the 3CX listing. 5060 is the standard value; if the email gives a different one, use that.
• Only your own account's numbers can be shown on outbound calls — "You can only present numbers associated with your account as Outbound Caller ID". Leave "Show as" empty — the line's number will be sent.

Sources: 3CX — SIP providers in Hong Kong · 58VOIP — SIP Trunk / DID — 10.09.2026.

28VOIP / Matrix Technology — a local provider and integrator#

The Hong Kong company Matrix Technology (HK) Ltd (Kwai Chung, tel. 3900 1928) is a 3CX integrator and maker of the Sipdex PBX, and under the 28VOIP brand a telephony provider whose SIP service is certified by 3CX for Hong Kong. Encrypted SIP (TLS) is not supported, and there is no self-service portal. It also resells HGC and HKBN trunks — but for a cloud PBX you need 28VOIP's own service.

What to enter in the admin panel

What to set up with the provider: order a trunk and a Hong Kong number → ask them to send the full number in incoming calls, not the short one → agree on G.711 codecs → check which numbers may be shown on outbound calls (only the account's numbers).

Pitfalls ⚠️

• A short number in incoming calls. Per the 3CX listing, the trunk number is entered "in the short number format (e.g. 4621)". If that is what arrives, the call is accepted but the PBX cannot pick the line by number, and it goes to the trunk's general route. With one number on the trunk this is harmless; with several, ask for the full number.
• Parameters by email only. Host, port and codecs are not published — take them from the activation email, not from 3CX templates.

Sources: 3CX — SIP providers in Hong Kong · 28VOIP — 10.09.2026.

HKT — a landline number over an internet trunk (check before ordering)#

The largest operator in Hong Kong (PCCW group), holding the most landline number blocks. The product is HKT Enterprise SIP Trunk; it is ordered through sales, and there are no tariffs or parameters on the website. There are two variants: the "local sip trunk" arrives over the HKT line into a second network card of the PBX, with private server addresses — it cannot be connected to a cloud PBX; the "Internet registration sip trunk" registers over the internet, and that is the one to order.

The parameters below come from a write-up by the partner 58VOIP dated 25.03.2025, not from an HKT document: check them against the connection form.

What to enter in the admin panel

What to set up with the provider: order the trunk in the internet variant, not "over the line" → get the Pilot DN, the number range and the password → before signing, ask in writing whether the trunk can work without SRTP → agree on the G.711 u-law codec.

Pitfalls ⚠️

• ⚠️⚠️ SRTP. The 58VOIP write-up says it plainly: "Since HKT only supports SRTP, this may cause outbound call failures". Our PBX does not support media encryption or TLS for trunks: if HKT will not provide a trunk without SRTP, the connection will not work.
• P-Asserted-Identity is mandatory. HKT expects the number in the P-Asserted-Identity header (in the form PilotDN@hkt-uc.com); without it, outbound calls from additional numbers fail. This option is enabled on the server side — contact support before the first outbound call.
• The registration interval must be at least 300 seconds. With a shorter one HKT answers 423 Interval too brief. If the registration line does not turn green and "Trunk diagnostics" shows this error, contact support.

Sources: HKT Enterprise SIP Trunk · 58VOIP — HKT internet trunk · 58VOIP — HKT "local" trunk — 10.09.2026.

Telcos: a trunk over their own line#

The other big operators sell a SIP trunk together with their own line to the office — to a PBX on the customer's premises. Whether a cloud PBX can connect has to be clarified before the contract. There is no "what to enter" table here: if the operator agrees to deliver calls over the internet to your "Static IP" (the "Server" tab), fill in the form from the sheet they send, and take the questions from "What to ask the provider".

• HKBN Enterprise Solutions — the only public set of parameters (a guide by the PBX maker Sipdex) shows the trunk inside the operator's private network: an HKBN gateway in the office, a SIP proxy with a 10.15.x.x address, a static route into the HKBN network, IP authentication without registration. A cloud PBX cannot reach such an address. ⚠️ The incoming number arrives as the last three digits of the range — the line cannot be told apart by number.
• HGC — "HGC SIP Trunk" to the customer's IP PBX, up to 850 channels on one interface; it also holds 5807 VoIP numbers. ⚠️ Parameters are not published, and the service is sold together with HGC access — request a trunk to a third-party address in the cloud explicitly. Order on the website or through partners (for example, 28VOIP / Matrix).
• ComNet Telecom (HK) — an operator with its own block of landline numbers; Enterprise SIP Trunk over the customer's broadband line, sales — 3503 3003. ⚠️ When the data was collected on 10.09.2026 the provider's website did not open; parameters are available only from a manager.
• China Mobile Hong Kong, SmarTone, 3 Hong Kong, China Unicom (Hong Kong), Verizon Hong Kong — they hold landline numbers and offer corporate voice, but there are no public instructions for connecting a third-party PBX. Confirm the status of the service with a manager.

Other local providers: parameters under contract#

• A-Z Telecom (AZ-TEL) — a Hong Kong IP telephony provider since 2009 (office on Nathan Road, branches on the mainland): "A-Z SIP Trunk" for 30–2000 simultaneous calls, regular and toll-free numbers in Hong Kong and on the mainland — handy if the venue has many guests from China. Neither parameters nor the connection mode are published: request them by email and check against "What to ask the provider" — especially transport (UDP/TCP) and codecs. ⚠️ As of 10.09.2026 the website's security certificate had expired, and the latest news on it dates from 2021.
• Deltapath — a Hong Kong developer of cloud telephony and holder of 5801 VoIP numbers. The retail "Hong Kong Anywhere Number" costs USD 7.8 per line per month, unlimited within Hong Kong, no contract; but the number lives in their cloud, and a SIP trunk to a third-party PBX is not offered publicly. The provider itself warns: no SMS, and the number cannot be ported.

International providers with Hong Kong numbers#

Cards for popular international providers are already in the catalogue when you add a provider — the server address and mode are filled in automatically. What is specific to Hong Kong:

• Twilio — listed by 3CX as the preferred provider for Hong Kong. Number types: mobile +852 9…, national +852 30… and +852 58…, toll-free +852 800…. National numbers are not sold to individuals — only to businesses: a business registration certificate, proof of the company's address (documents issued within the last 3 months), a website or social media page. A local address is not needed — the address may be in any country.
• DIDWW — holder of the 5809 VoIP range. Its Hong Kong page offers +852 58… numbers: incoming calls, emergency calls and incoming fax are supported, SMS and number porting are not.
• Bandwidth (Voxbone) — holds four VoIP ranges (5803, 5806, 5808, 5819): the largest holder of Hong Kong VoIP numbers among international providers.
• Tata Communications — a wholesale operator certified by 3CX for Hong Kong: the number arrives in international format, no TLS. Sold under contract through a manager — too much for a single venue.
• PBX.IM — a Hong Kong offering with 2/3 landline numbers, 58 VoIP numbers and 800 toll-free numbers, self-service sign-up; trunk parameters and mode appear in the portal after ordering.
• AstraQom — published prices as of 10.09.2026: from USD 10 per month (1 number, 1 line, 100 minutes) to USD 48 (2 lines, 1000 minutes), an extra number USD 7.50 per month, activation in 1–3 business days, Asterisk support stated. ⚠️ One or two lines means one or two simultaneous calls: too few for a venue with a call queue.
• Telnyx, DIDLogic, Zadarma, Sonetel and other aggregators — Hong Kong numbers are in their coverage, usually from the 58 series.
• ⚠️ A general caveat. International providers almost always give a 58-series number — without portability. A 2/3 landline number comes from local Class 1 operators (HKT, HGC, HKBN, ComNet) or their resellers, and among international providers — from those who explicitly list the 2/3 series (like PBX.IM).

Number porting#

• Only Class 1 numbers can be ported — 2/3 landlines and mobiles: between ordinary fixed-line service, first-class IP telephony and Class 1 providers. The request is filed by the receiving operator; timelines and documents are in its form — confirm when ordering. AstraQom, for example, quotes 2–4 weeks.
• ⚠️ 58-series (Class 2) numbers cannot be ported anywhere — neither to another Class 2 provider nor back to landline service. Moving from a landline number to Class 2 also means losing the number.
• The practical takeaway: if the number is printed on the menu and the sign, take a 2/3 landline from a Class 1 licensee (or port your existing one), not a cheap 58 number from an aggregator.
• Register the number to the company, not to an employee — otherwise it leaves with them.

Rules and paperwork#

If it does not work#

1. The operator says "the trunk is up", but "Test connection" fails. Most likely you were given a trunk over the operator's line: for HKBN and the "local" HKT variant the server address is inside their private network. It cannot be connected to a cloud PBX — you need an internet trunk (58VOIP, 28VOIP, the HKT internet variant).
2. HKT: registered, but outbound calls fail. Check two things: whether the trunk requires SRTP (it will not work with our PBX) and whether P-Asserted-Identity is enabled — support turns it on.
3. HKT: registration is rejected with 423 Interval too brief. The operator requires a registration interval of at least 300 seconds — contact support.
4. The call connects, but there is silence. Check the codecs: you need G.711 (a-law or u-law) or G.722, our PBX has no G.729.
5. Incoming calls arrive, but on the wrong line. Check the format in which the provider sends the number (short at 28VOIP, the last three digits at HKBN) and whether the last seven digits of two of your numbers coincide.
6. 999 cannot be dialled. Three-digit numbers do not go out through a trunk — you need an ordinary phone for an emergency call.

General 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 58VOIP: the registrar address for Hong Kong is published (siphk.58voip.com), and the mode is registration over UDP, so the form can be filled in completely. The fallback is 28VOIP / Matrix with the same mode. If you specifically need a 2/3 landline number — HKT in the internet variant, but only after a written answer that the trunk works without SRTP.

Why can I not simply take a trunk from HKBN or HGC?#

Because they sell the trunk together with their own line to the office: in HKBN's published guide the SIP proxy sits in the operator's private network and needs a static route into it, while HGC publishes no parameters and sells the service together with its own access. Our PBX is in the cloud and has no such line. If the operator agrees to deliver calls over the internet to your static IP, it can be connected — but ask before signing.

What is worse about a 58 number compared with a landline?#

It is a Class 2 VoIP number: it works the same way, but cannot be ported — the number disappears when you change provider, and the provider is not obliged to offer directory service. For a number printed on the sign and the menu, a 2/3 landline is safer.

Do I need a Hong Kong company?#

No. The licence is held by the provider, and international sellers (for example, Twilio) do not require a local address — business registration and proof of the company's address are enough. Twilio does not sell national numbers to individuals.

Can I call guests showing a Hong Kong number?#

Yes, through the provider of that number and only with the numbers of your contract. A call with a Hong Kong number sent via a foreign route arrives with a "+" in caller ID and looks suspicious.

Sources#

All links were checked on 10.09.2026.

Regulator and numbering

• OFCA — Know More about IP Telephony Service (Class 1 / Class 2): https://www.ofca.gov.hk/en/consumer_focus/guide/general/ipts/index.html
• OFCA — Numbering Plan for Telecommunications Services in Hong Kong, issue 1.9.2026 (PDF): https://www.ofca.gov.hk/filemanager/ofca/en/content_311/no_plan.pdf
• OFCA — Insertion of "+" Sign in the Calling Number Display: https://www.ofca.gov.hk/en/consumer_focus/guide/general/telephone_scams/index.html
• Hong Kong Government — press release on the "+" in caller ID, 20.08.2015: https://www.info.gov.hk/gia/general/201508/20/P201508200536.htm
• Communications Authority — Guidance Note for Application for SBO Licence (PDF): https://www.coms-auth.hk/filemanager/common/licensing/SBO-Guideline.pdf

Providers

• 3CX — SIP providers in Hong Kong (Twilio, 28VoIP, 58VoIP, Tata): https://www.3cx.com/partners/sip-trunks/hong-kong/
• 58VOIP — SIP Trunk / DID: https://en.58voip.com/china-sip-trunk/
• 28VOIP (Matrix Technology HK): https://www.28voip.com/
• HKT — Enterprise SIP Trunk: https://www.hkt-enterprise.com/en/products-solutions/unified-communications/voice/solution/hkt-enterprise-sip
• 58VOIP — connecting the HKT internet trunk: https://en.58voip.com/3cx-server-connects-with-hkt-internet-registration-sip-trunk/
• 58VOIP — connecting the HKT "local" trunk: https://en.58voip.com/3cx-server-connects-with-hkt-local-sip-trunk/
• HGC — SIP Trunk: https://www.hgcbiz.com/products-and-services/voice/sip-trunk
• HKBN Enterprise Solutions — Enterprise SIP Trunk (PDF): https://www.hkbnes.net/uploads/support/ProductCatalogue/EnterpriseSIPTrunk.pdf
• Sipdex — HKBN trunk configuration: https://sipdex.com/ippbx/index.php/chapter-14-hkbn-sip-trunk-configuration-pstn/
• ComNet Telecom (HK) — SIP Trunk Solution: https://www.comnet-telecom.com.hk/en/sip-trunking-enterprisesolution/
• A-Z Telecom — A-Z SIP Trunk: https://www.link-az.com/a-z-sip-trunk/
• Deltapath — Hong Kong Anywhere Number: https://www.deltapath.com/product/hong-kong-anywhere-number/

International numbers

• Twilio — regulatory requirements for Hong Kong: https://www.twilio.com/en-us/guidelines/hk/regulatory
• DIDWW — Hong Kong +852 (58) National: https://www.didww.com/phone-numbers/all-phone-numbers/Hong_Kong/National
• PBX.IM — Hong Kong SIP Trunking: https://www.pbx.im/services/sip-trunking-provider/hk
• AstraQom — SIP Trunks in Hong Kong: https://www.astraqom.com/hk/hong-kong-sip-trunks/
• Hong Kong Free Press — on the OFCA code of practice and suspended numbers, 30.03.2024: https://hongkongfp.com/2024/03/30/spam-or-scam-how-unwanted-phone-calls-from-salesmen-or-crooks-plague-hongkongers-despite-countermeasures/

Related pages#

• Connecting a provider's number to the PBX — general steps, trunk modes, network, connectivity check.
• SIP phone setup — how to connect desk phones and DECT to extensions.