To create this lab, some experience with Asterisk is required for the voicemail integration. This lab is relatively hard to implement. Some IP phones hardly ever send the busy message, because they have more than a single line. It is important to use all the lines before to get the "486 busy" message. There is an IP phone from SNOM that has a wonderful busy button to indicate to the user that the phone is busy. We will reduce the INVITE timeout to make the tests easier and less cumbersome. On production environments remove these instructions.

modparam("tm", "fr_timer", 5)
modparam("tm", "fr_inv_timer", 20)

Step 1: Test the call forward for unanswered calls.

Call from extension 1000 to extension 1002. The call should go to the voicemail system, with the unavailable message.

Step 2: Test the call forward on busy.

Take extension 1003 off-hook. Call extension 1003 from extension 1000. It should go to the voicemail system with the busy message.