---
title: "How do I forward my office phone to my mobile when I'm out?"
topic: "Business & Teams"
updated: 2026-05-09
canonical: https://acrobits.net/resources/knowledge-base/how-do-i-forward-my-office-phone-to-my-mobile-when-im-out/
summary: "Yes. Almost every modern PBX (3CX, FreePBX, Asterisk, Cisco BroadWorks, RingCentral, Zoom Phone, NetSapiens) supports 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)."
---

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

> Yes. Almost every modern PBX (3CX, FreePBX, Asterisk, Cisco BroadWorks, RingCentral, Zoom Phone, NetSapiens) supports 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).

Traditional call forwarding sends office calls to your cell number — but you lose every PBX feature in the process: no transfer back to a colleague, no conferencing, no internal directory, and the caller sees your personal mobile number when you call back. The better approach is to put your office extension on your phone directly using [**Groundwire**](/sip-client-ios-android/). Your mobile becomes the extension, not a forwarded destination.

## Forwarding vs softphone — the difference that matters

Traditional call forwardingGroundwire as mobile extension

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

## Step-by-step — 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: G.722 primary on Wi-Fi for HD voice, G.729 fallback on cellular for low-bandwidth networks. Groundwire switches automatically based on 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. Almost every modern PBX (3CX, FreePBX, Asterisk, Cisco BroadWorks, RingCentral, Zoom Phone, NetSapiens) supports 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?

Nothing. 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 — one tap.

## Will the call quality hold up on cellular?

Generally yes on 4G/5G, occasionally rough on weak 3G. 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 (Wi-Fi to cellular as you walk out of the office) without dropping the call — most softphones drop on handover.

## Does this work outside my home country?

Yes — and this is where it beats traditional forwarding badly. 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

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

  - **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).

## Bottom line

Don't forward — extend. Putting Groundwire on your phone gives you the full PBX feature set wherever you are, with proper office caller ID, no roaming charges, and one-tap toggling when you're back at your desk. Need to roll 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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