Connect Zoiper softphone to a NumberGroup SIP trunk (mobile + desktop)

Zoiper 5 is the most popular cross-platform softphone for direct SIP-trunk registration. Free version is enough for a single SIP account; pay-once licences unlock multi-account, codecs and encryption. Works the same way on iOS, Android, Windows, macOS and Linux — set it up once, get a UK business number on your laptop or mobile.

When you ask us to set up the trunk, mention you want the User-Agent Type set to "RFC3261 Standard Trunk" and Send Numbers As to "United Kingdom" — Zoiper shows the incoming CLI in the familiar UK format, and CallKit on iOS recognises it as a normal phone number.

The quick path (Manual SIP account)

Zoiper has a setup wizard, but it won't recognise NumberGroup as a preset provider. Skip the wizard, add the account manually— that's the working path:

• iOS / Android: Settings → Accounts → + (add) → SIP account → Manual
• Windows / Mac / Linux: Settings → Accounts → Add → Manual configuration → SIP

Step 1: account configuration

• Account name: NumberGroup (your reference)
• Domain: sip.numbergroup.com
• Username: T-AAAAAA-NNN from the email we send you (e.g. T-102377-001)
• Password: your trunk password
• Authentication username: same as Username
• Outbound proxy: leave blank
• Caller ID: your business name (optional — shown on outbound where the network allows)

Hit Register. Status switches to green / Registered within a few seconds.

Step 2: network & codec settings

Under the account settings → Network Settings / Advanced:

• Transport: UDP
• Use STUN: yes (Zoiper's default STUN server works fine)
• SRTP: disabled (unless you've set the trunk Voice Mode to "secure encrypted voice")
• DTMF mode: RFC 2833

Under Audio codecs: enable PCMU, PCMA and G722 in that order. Disable anything else for predictable quality.

Step 3 (mobile): push notifications

A common Zoiper-on-mobile question: why don't incoming calls ring when the app is in the background?

By default Zoiper keeps a persistent SIP registration in the background, which drains battery. To save battery, Zoiper uses push notifications to wake up — but push only works on the paid Zoiper version and requires their push proxy.

Two ways to handle this:

• Pay for Zoiper Premium — push works properly, ~£8 one-off per platform. Recommended for business use.
• Keep Zoiper in the foreground on critical phones. Battery hit, but free.

On iOS, also make sure Background App Refresh is on for Zoiper and the notification permission is granted.

Step 4 (iOS): CallKit integration

Zoiper supports Apple CallKit — incoming SIP calls appear on the iPhone lock screen exactly like a normal phone call, land in the Recents app, and respect Do Not Disturb. Enable it under Settings → CallKit Integration. Highly recommended; makes Zoiper feel native.

Step 5: test

• Dial out: ring your own mobile from Zoiper. Confirm Caller ID matches your trunk's Default CLI.
• Dial in: ring your NumberGroup DDI from a mobile. Zoiper should ring within 2 seconds.
• When you ask us to set up the trunk, the trunk's Registered field should say "registered".

When it doesn't work

Status stuck on "Registering"

• Wrong username/password — re-check the email we sent with your trunk credentials
• Domain typo — must be sip.numbergroup.com exactly
• On a hotel / public Wi-Fi network that blocks SIP — try a personal hotspot

Outbound rejected with 403

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

Calls connect but one-way audio

• Re-enable STUN in Zoiper's account settings
• On Android, grant Microphone permission
• On corporate Wi-Fi, ask IT if SIP/RTP ports are open

Calls ring on Zoiper desktop but not mobile

• Mobile Zoiper Free won't reliably ring in the background — see push notification section above
• Same SIP account registered on multiple devices is OK — the call will fork to all registered endpoints

Multi-device tip

You can register the same Authorisation ID on multiple devices (desk phone + laptop Zoiper + mobile Zoiper). Incoming calls ring all of them simultaneously. First one to pick up takes the call.

For more sophisticated routing — different teams ringing different devices at different times of day — Membership includes a hosted PBX that handles this without you having to register every endpoint individually.

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