asterisk users - Jul 2003 - Music while waiting for agent to free.

I has a E1 trunk to PC and 4-5 SIP phones.
Can * plays some music in all calls if all the phones are busy, and when one got
free, to forward the call to the agent.
Excuse me, if it is newbie question, but i'm googling and reading this list
4 hours and didn't found clear answer :)