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SIP trunking · 6 min read

Connect a Yealink desk phone to a NumberGroup SIP trunk

Register a Yealink T-series IP phone (T31, T33, T46, T54) directly to a NumberGroup SIP trunk — web UI walkthrough, codec settings, NAT, dial-plan and the firmware version gotcha to know.

This is the setup for registering a Yealink IP desk phone directly to a NumberGroup SIP trunk (no PBX in between). Works on the modern T-series: T31, T33, T46, T48, T53, T54, T57. About 5 minutes once you have the phone's web UI open.

When you ask us to set up the trunk, mention you want the User-Agent Type to "RFC3261 Standard Trunk" and Send Numbers As to "United Kingdom" — Caller ID then shows in the familiar 01214001262 format the phone's LCD reads cleanly.

What you'll need from us

The credentials and settings your device needs to register against the NumberGroup SIP trunk are:

  • Domain / registrar: sip.numbergroup.com
  • Authorisation ID (also called SIP username): looks like T-AAAAAA-NNN e.g. T-102377-001
  • Password: a random string we generate per trunk
  • User-Agent Type: we set this our side to match your device (e.g. 3CX Phonesystem, DDI in R-URI (Asterisk), RFC3261 Standard Trunk) so DDIs present in the format your equipment expects
  • Send Numbers As: also set our side — pick the format that works best for your platform:
    • International (+xx) — true E.164 (+441214001262) for 3CX, Cisco, Yealink and most modern PBXs
    • International (xx) — bare digits (441214001262) for Asterisk / FreeSWITCH dialplan regex
    • United Kingdom — UK format (01214001262) for direct-register desk phones / softphones where humans read the Caller ID
  • Allowed IPs (optional): for an extra security layer we can lock the trunk to only register from your office IPs — tell us which when you ask

Once you have the credentials, the rest of this guide walks through the device-side config. If you'd rather skip the config altogether, ask us — we'll do it for you on most common PBXs and phones.

Step 1: log in to the web UI

  • Find the phone's IP: Menu → Status on the handset.
  • Browse to http://192.168.x.y from a computer on the same LAN.
  • Login: default is admin / admin (older firmware) or a sticker-printed password on newer firmware. Change it immediately.

Step 2: account configuration

Go to Account → Register → Account 1:

  • Line Active: Enabled
  • Label: NumberGroup (display label)
  • Display Name: your business name
  • Register Name: T-AAAAAA-NNN (e.g. T-102377-001)
  • Username: same as Register Name
  • Password: your trunk password from the email we send you
  • SIP Server 1 → Server Host: sip.numbergroup.com
  • SIP Server 1 → Port: 5060
  • SIP Server 1 → Transport: UDP
  • SIP Server 1 → Server Expires: 3600
  • Outbound Proxy Server: Disabled
  • NAT → STUN: Disabled (NumberGroup's symmetric RTP handling means STUN is unnecessary)

Hit Confirm.

Step 3: codec settings

Account → Codec → Account 1:

  • Enable, in order: PCMU, PCMA, G722, G729
  • Disable everything else for predictable quality

G722 is HD voice — Yealink phones handle it cleanly and NumberGroup passes it end-to-end where the other side supports it.

Step 4: advanced account settings

Account → Advanced → Account 1:

  • DTMF Type: RFC2833
  • DTMF Payload Type: 101
  • Subscribe MWI: Disabled (unless you use NumberGroup voicemail)
  • Subscribe MWI to Voice Mail: Disabled
  • Voice Mail Number: *88 (if you use NumberGroup voicemail)
  • RTP Encryption (SRTP): Disabled (unless trunk Voice Mode = secure encrypted voice)
  • Keep Alive Type: Default
  • Keep Alive Interval (Seconds): 30
  • RPort: Enabled

Step 5: dial plan

Sensible UK dial plan so the phone auto-dials when you stop typing. Features → Dial Plan → Dial Now (or Replace Rule depending on firmware):

  • UK area codes (10-digit after 0): 0[1-9]xxxxxxxxx
  • Mobiles (11-digit after 0): 07xxxxxxxxx
  • Freephone & UK-wide: 0[38]00xxxxxx and 0[38]xxxxxxxxx
  • International: 00x.
  • Emergency: 999|112|101
  • NHS: 111
  • Short codes / feature codes: *x.

Step 6: verify

  • The LCD should show your label and a registration tick within a few seconds
  • The NumberGroup team can confirm the trunk has registered our side — ring us or check the email we sent confirming the trunk is live
  • Dial out to your mobile to confirm Caller ID
  • Ring your DDI from a mobile to confirm inbound

Firmware gotcha

Yealink firmware older than 84 (T46S, T48S, T54W) has a SIP re-INVITE quirk that can cause one-way audio on transfers. Upgrade to the latest firmware available for your model before going live — Yealink's support portal hosts every version. Newer T31/T33/T53/T57 series ship with current firmware and are fine out of the box.

When it doesn't work

Account icon shows red / "Register Fail"

  • Wrong Register Name or Password — double-check on the trunk
  • Wrong Server Host — must be sip.numbergroup.com exactly
  • Outbound UDP 5060 blocked on your network firewall

Calls connect but one-way audio

  • Re-enable RPort under Advanced
  • Disable SIP ALG on the router
  • Confirm STUN is set to Disabled (it can cause issues with our symmetric RTP)

Outbound rejected with 403

Your Default CLI on the trunk isn't set to one of your DDIs. Fix on the trunk.

Set fraud caps before going live

Single-handset phones should never have more than 1–2 simultaneous calls. Set Fraud Detection Simultaneous Calls to 2 and Daily Spend to a sensible ceiling. See our telecom fraud guide.

Source: the device navigation in this guide follows Yealink Support — search your T-series model's admin guide. We keep the click-path with the manufacturer so it stays current — the NumberGroup trunk values above are the part specific to your account.

Want phones at supplier cost?

Members get Grandstream desk phones at our distributor price (£28 – £83 ex-VAT). Yealinks too if you ask — supplier cost, no handset markup.

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