Connect a Snom desk phone to a NumberGroup SIP trunk
Map your NumberGroup SIP trunk credentials to the right fields on a Snom D-series desk phone (D717, D735, D785, D862). Field-by-field mapping table plus a link to Snom's own web-UI guide.
This registers a Snom D-series desk phone directly to a NumberGroup SIP trunk — no PBX in between. It applies across the current D-series (D717, D735, D785, D862 and siblings), where every setting lives under a per-line Identity rather than a single global account page.
When you ask us to set the trunk up, request Send Numbers As set to "United Kingdom" so Caller ID arrives in the familiar 01214001262 format the Snom screen reads cleanly.
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-NNNe.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
- International (+xx) — true E.164 (
- 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.
Field mapping
We don't reproduce Snom's menus here — they own that and keep it current. The table below maps each value we send you to the exact Snom field it belongs in.
Find the phone's IP on the handset (press the gear key → Information → System Information), browse to it from a computer on the same LAN, then open Identity 1 in the left menu — the Login, SIP and RTP tabs hold everything below.
Full navigation is in the manufacturer's own guide: Snom Service Hub — accessing the phone web interface (WUI). We keep the click-path with them so it stays current — the table below is the part that's specific to your NumberGroup trunk.
| NumberGroup value | Snom D-series field |
|---|---|
| sip.numbergroup.com | Registrar (Identity 1 → Login) |
| T-AAAAAA-NNN | Account (Identity 1 → Login) |
| T-AAAAAA-NNN | Authentication Username (Identity 1 → Login) |
| your trunk password | Password (Identity 1 → Login) |
| UDP / 5060 | Transport / Registrar port (Identity 1 → SIP / NAT) |
| RFC2833 | DTMF — RFC2833 (Identity 1 → RTP) |
| STUN off, rport on | NAT / SIP behaviour (Identity 1 → SIP) |
| PCMU, PCMA, G722, G729 | codec list (Identity 1 → RTP); disable SRTP |
| *88 | Voicemail number, if you use NumberGroup voicemail (Identity 1 → SIP) |
Split-field note: Snom separates Account (the SIP user) from Authentication Username (the auth ID). On a NumberGroup trunk both take the same value — your T-AAAAAA-NNN.
Verify
- The screen shows a registered tick against the identity within a few seconds
- We can confirm the trunk has registered our side — ring us or check the email confirming the trunk is live
- Dial your mobile to confirm Caller ID; ring your DDI from a mobile to confirm inbound
If it won't register
- Wrong Account or Password — re-check against the trunk email
- Registrar must be
sip.numbergroup.comexactly - Outbound UDP 5060 blocked on your network firewall
- One-way audio: confirm Symmetric RTP / rport behaviour, disable SIP ALG on the router, leave STUN empty
- Outbound rejected with 403: your Default CLI on the trunk isn't one of your DDIs — fix on the trunk
Set fraud caps before going live
A single desk phone should never place more than 1–2 simultaneous calls. Ask us to set Fraud Detection Simultaneous Calls to 2 and a sensible Daily Spend ceiling. See our telecom fraud guide.
Phones at supplier cost
Members get Grandstream desk phones at our distributor price (£28 – £83 ex-VAT), and we'll provision a Snom, Yealink or Fanvil you already own at no extra charge.