A common query for people implementing IP based phone systems is how to have a phone ring differently for internal (from within the office) and external (from the PSTN) calls. To do this you'll need two things; a phones that supports this - here we're using Yealink phones, and a VoIP server that supports the "Alert-info" header - many do such as the popular open source solutions Asterisk and FreeSWITCH. Other than that it's all pretty straight forward.

Firstly we will configure the Yealink phone. To do this go to the "Phone" tab and then to the "Ring" page under that.

Once there add an entry into the first set of boxes. Under "Internal Ringer Text" choose a short descriptive name for the ring, I've called it "Internal" as I'm going to use it to change the ringer for internal calls. Under "Internal Ringer File" select the ring that you would like to use. That's it as far as the Yealink phone configuration goes.

Configuring the VoIP PBX differs depending on the SIP server you are using. For Asterisk you need to add a line to the extension or incoming rule configuration such as the following;

exten => s,1,SIPAddHeader(Alert-Info: <http://localhost/>;info=Internal)

The "Internal" at the end of that line correlates to what was entered into the phone configuration. This can be added either directly into the configuration file, or perhaps through the GUI interface that your PBX provides.

For FreeSWITCH things are much the same with a slightly different syntax. Add a line to the extension rule such as the following;

<action application="export" data="alert_info=<http://localhost/>;info=Internal"/>

Again the "Internal" at the end of that line correlates to what was entered into the phone configuration.

This is all the configuration you need, you can set up as many different rings as your phone and VoIP PBX system allow.