---
title: "How do I forward my office phone to my mobile when I'm out?"
topic: "Business & Teams"
updated: 2026-07-09
canonical: https://acrobits.net/resources/knowledge-base/how-do-i-forward-my-office-phone-to-my-mobile-when-im-out/
summary: "Use Groundwire to register your office extension directly on your phone. Your mobile becomes the extension, not a forwarded destination, so you keep the full PBX feature set on the go: transfer back to a colleague, conferencing, internal directory access, and office caller ID on callbacks. Traditional call forwarding only sends office calls to your cell number, and you lose many of those PBX features in the process."
---

# How do I forward my office phone to my mobile when I'm out?

> Use Groundwire to register your office extension directly on your phone. Your mobile becomes the extension, not a forwarded destination, so you keep the full PBX feature set on the go: transfer back to a colleague, conferencing, internal directory access, and office caller ID on callbacks. Traditional call forwarding only sends office calls to your cell number, and you lose many of those PBX features in the process.

Use [**Groundwire**](/sip-client-ios-android/) to register your office extension directly on your phone. Your mobile becomes the extension, not a forwarded destination, so you keep the full PBX feature set on the go: transfer back to a colleague, conferencing, internal directory access, and office caller ID on callbacks. Traditional call forwarding only sends office calls to your cell number, and you lose many of those PBX features in the process.

## Forwarding vs a mobile softphone

Traditional call forwardingGroundwire as your office extension on mobile

How it worksPBX dials your cell numberPhone registers as a SIP extension
Caller ID on outboundYour personal mobile numberYour office number
Transfer to colleagueNoYes (blind + attended)
ConferenceNoYes
Internal directory / BLFNoYes
VoicemailCarrier voicemailOffice voicemail
Cost per forwarded callPer-minute charge from PBXFree (data only)
Works internationallyExpensive roamingFree over Wi-Fi anywhere

## Set up Groundwire as your office extension

  - **Get SIP credentials from your PBX admin.** Either reuse your desk phone's credentials (if your PBX supports multi-device registration, most do) or ask for a new mobile-specific extension.

  - **Open Groundwire → Settings → Accounts → Add account → Generic SIP.**

  - Enter the SIP server, username, password, and transport (TLS recommended; UDP/TCP if your PBX requires it).

  - Set codecs to match your network: G.722 on Wi-Fi for HD voice, and G.729 as a low-bandwidth fallback on cellular. Groundwire can switch between them based on the connection type.

  - **Enable push notifications** in Groundwire and at the OS level: this is what makes the app ring when it's closed.

  - Test: have a colleague call your extension. Both your desk phone and Groundwire should ring simultaneously.

## Can my desk phone and Groundwire both ring?

Yes. Many modern PBXs, including 3CX, FreePBX, Asterisk, Cisco BroadWorks, RingCentral, Zoom Phone, and NetSapiens, support multiple registrations per extension. Both devices register, both ring, you answer on whichever you're closest to. Some PBXs also let you set a ring-delay sequence (desk phone first, Groundwire after 3 rings if no answer).

## What changes when I'm back in the office?

In most setups, nothing changes. Groundwire and your desk phone coexist. There are no forwarding rules to toggle. If you don't want Groundwire to ring while you're at your desk, set it to **Do Not Disturb** in the app with one tap.

## Will the call quality hold up on cellular?

Call quality is usually good on 4G/5G and can be rough on weak 3G coverage. Groundwire lets you configure codecs separately per network type:

  - **Wi-Fi:** G.722 (HD, 64 kbps): sounds better than landline

  - **Cellular:** G.729 (low bandwidth, 8 kbps): works on weak signal

Groundwire also handles network transitions, such as moving from Wi-Fi to cellular, without dropping the call. Many softphones are less reliable during handover.

## Does this work outside my home country?

Yes, and this is where it is especially useful compared with traditional forwarding. Forwarding an office call to a mobile abroad usually means international per-minute charges from the PBX side and roaming charges from the mobile carrier. Groundwire over Wi-Fi (hotel, coworking, café) costs nothing extra.

## Security and privacy with SIP, SRTP, and ZRTP

Groundwire supports TLS for SIP signalling and SRTP for media: match whatever your PBX requires. For end-to-end encrypted calls between two Groundwire users, enable ZRTP. Encryption is opt-in per account, so you can run a corporate extension and a private encrypted line side by side.

## Troubleshooting common Groundwire setup issues

  - **App doesn't ring when closed:** push notifications not enabled. Check Groundwire settings and iOS/Android system permissions.

  - **Outbound caller ID shows internal extension number:** your PBX needs to set the outbound caller ID; this is a PBX config, not Groundwire.

  - **Audio drops when leaving Wi-Fi:** most PBXs need session timers (RFC 4028) enabled to refresh the registration during handover. Enable in Groundwire account settings.

  - **Both devices ring but only one can answer:** confirm your PBX supports parallel ringing (most do; some require an explicit "ring all devices" setting on the extension).

## Why extending the office extension works better

Extend the extension to your phone instead of forwarding calls. Groundwire gives you the full PBX feature set wherever you are, with office caller ID, no roaming charges, and one-tap toggling at your desk. Rolling this out across a team? See [how to get your team receiving calls from your business phone system](/resources/knowledge-base/how-do-i-get-my-team-to-receive-calls-from-our-business-phon/).

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