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SIP trunking · 6 min read

Connect a Poly (Polycom) VVX desk phone directly to a NumberGroup SIP trunk

Register a Poly VVX 150 / 250 / 350 / 450 (formerly Polycom) directly to a NumberGroup SIP trunk — web UI walkthrough, line config, codec list, dial-plan, NAT, and the UC software version that matters.

This is the setup for registering a Poly VVX desk phone (formerly Polycom — same phone, rebranded after the HP acquisition) directly to a NumberGroup SIP trunk. Works on the modern VVX 150, 250, 350, 450 — and the older VVX 300/310, 400/410, 500/501 with current UC Software.

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" — Poly VVX handsets render the human-readable 01214001262 format better on the LCD than +44 prefixed numbers.

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: check the UC Software version

Poly VVX needs UC Software 6.x or later for reliable modern-TLS SIP and the latest codec list. Older phones still work but ship with 5.x — upgrade before going live.

  • On the phone: Menu → Status → Platform → Phone → check Application version
  • If < 6.x, download the latest UC Software ZIP from poly.com support
  • Upgrade via the web UI: Utilities → Software Upgrade

Step 2: log in to the web UI

  • Find IP: Menu → Status → Network → TCP/IP Parameters
  • Browse to https://192.168.x.y (Poly forces HTTPS — accept the self-signed cert)
  • Default admin password on newer firmware: 456 (or the password printed on a sticker on the back). Change it immediately.

Step 3: configure Line 1

Settings → Lines → Line 1:

Identification

  • Display Name: your business name (shows on LCD)
  • Address: T-AAAAAA-NNN (e.g. T-102377-001) — yes, in the "Address" field, this is the SIP user part
  • Label: NumberGroup (line button label)
  • Type: Private
  • Third Party Name: leave blank
  • Number of Line Keys: 1 (or more for shared call appearance)
  • Calls Per Line Key: 4 (or up to 24)

Outbound Proxy

  • Address: leave blank

Server 1

  • Address: sip.numbergroup.com
  • Port: 5060
  • Transport: UDPOnly
  • Expires: 3600
  • Register: 1 (Yes)
  • Retry Time Out: 0 (use exponential backoff default)
  • Retry Max Count: 3
  • Subscribe Expires: 3600
  • Special Interop: Standard

Authentication

  • User ID: T-AAAAAA-NNN (same as Line Address)
  • Password: your trunk password from the email we send you

Click Save. The line key on the phone should light green within a few seconds.

Step 4: codec preferences

Settings → SIP → Audio Codec Priority (or per-line under Voice Settings depending on UC version):

  • Enable, in priority order: G.711µ-law, G.711a-law, G.722, G.729AB
  • Disable Opus / Siren unless you have a specific reason — most PSTN gateways won't negotiate them

Step 5: NAT & network

Settings → SIP → Local Settings:

  • NAT Keepalive Interval: 30
  • NAT IP Address: leave blank (auto)
  • Out-Of-Dialog REFER: Disable
  • STUN Server: leave blank — NumberGroup's symmetric RTP handling means STUN is unnecessary

On your router: disable SIP ALG. Almost always wrong.

Step 6: dial plan

Settings → SIP → Local Settings → Dial Plan (or under Preferences → Dial Plan on newer UC software). Sensible UK pattern:

  • Digit Map: *xx|999|112|111|101|0[1-9]xxxxxxxxx|07xxxxxxxxx|0[38]00xxxxxx|00xx.|x.T
  • Digit Map Timeout: 3

Step 7: verify

  • LCD shows registered line with green icon
  • We confirm the trunk has registered our side
  • Dial out to your mobile to confirm Caller ID
  • Ring the DDI from a mobile to confirm inbound

When it doesn't work

Line key icon is red / "Not Registered"

  • Wrong Authentication User ID or Password — re-check the email we sent with your trunk credentials
  • Wrong Server Address — must be sip.numbergroup.com exactly
  • Office firewall blocking UDP 5060
  • UC Software too old — upgrade to 6.x+

One-way audio

  • Disable SIP ALG on the router (the #1 cause)
  • Confirm NAT Keepalive is set
  • STUN should be blank — it can confuse the symmetric RTP

Outbound rejected with 403

Your trunk's Default CLI on the trunk isn't set to a valid DDI. Fix on the trunk.

Set fraud caps

Single desk phone — Fraud Detection Simultaneous Calls = 2, Daily Spend low ceiling. See our telecom fraud guide.

Source: the device navigation in this guide follows Poly Support — VVX business IP phones. We keep the click-path with the manufacturer so it stays current — the NumberGroup trunk values above are the part specific to your account.

Get phones at supplier cost

Members get Grandstream desk phones at our distributor price (£28–£83 ex-VAT). Polys, Yealinks and Cisco IP phones can be sourced at trade cost too — ask the team.

See hardware pricing →See what Membership includes →
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