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Configuring iSip (Connects Apple iPhone) for 3CX Phone System

IMPORTANT This guide has been tested with the following firmware versions:

Apple iPhone 2G version 2.2
iSip (formerly SipPhone on iPhone) version 2.0.3

Be aware that different firmware revisions may have different web interface formats and functionality.

iSip (formerly SipPhone on iPhone) is a native SIP/VOIP application for the iPhone. It is available from the iTunes App Store for a small fee (5 euros / 6USD). With iSip (formerly SipPhone on iPhone), the SIP connection is made directly to 3CX, so no ‘middle-man’ such as Fring is involved. This makes the call quality excellent.

This guide shows you how to setup the Apple iPhone as an external extension. If you need to use it internally on your LAN, you must create a separate profile, switch off STUN and adjust the IP/FQDN accordingly. The first SIP Account in the “Account Manager” will be always chosen for outbound calls when activated.

Due to the fact that SIP is blocked by default from the mobile providers the use of a WiFi connection is necessary.Make sure that you have an active WiFi Connection and you can access the Internet over it.

Installing iSip (formerly SipPhone on iPhone)

  1. To install the application visit the AppStore via iTunes or your iPhone. Search for “iSip (formerly SipPhone on iPhone)”.

Setting up iSip (formerly SipPhone on iPhone) with 3CX

  1. Start the iSip (formerly SipPhone on iPhone) by clicking on this Icon
  2. Configure the STUN server setting: Go to Settings and turn Stun on and set the Stun Server to “”. The rest of the settings on this page can be left on default.
  3. Now add 3CX Phone System as a SIP Provider by selecting “Accounts” from the bottom menu and then press “Edit”.
  4. Select “Add new SIP acco…”
  5. Select “other provider”
  6. Now enter the Sip Account settings.
    Domain – Enter the external IP or FQDN of your 3CX Phone System Server
    Username – Enter the Authentication ID of your extension (by default this is your extension number)
    Password – Enter the Authentication Password for this extension
  7. Enter the Voice Mail Number under ‘Advanced’.
    By default this is 999.
  8. Now click on “SIP Account” and then “Save” in the top bar.
  9. You will return to the Account Manager. By default the account is now added but not enabled. Slide the small bar next to the account name until the blue field will be visible. Your account is now ready to use.
  10. To verify that your SIP account has been correctly setup, Click on the Dialer – and check that the ‘SIP’ button is green. If yes, your account is correctly set-up and ready to use. Dial 999 and choose SIP to test your connection. You should be answered by your voice mail box.

SIP Phone Configuration Guides (Preferred)

SIP Phone Configuration Guides (Supported)

Free for up to 1 year! Select preferred deployment:


for Linux on a $200 appliance or as a VM

Get the ISO


for Windows as a VM

Download the setup file

On the cloud

In your Google, Amazon, Azure account

Take the PBX Express