asterisk users - Jun 2005 - Call group channel limits

I have a question that I've so far been unable to find the answer to:

Using an E1 interface for my PSTN connection I want to setup 5 SIP
phones in a call group (with a unique number for inbound calls) but only
allow the call group to receive a maximum of 3 calls at any one time.

Does Asterisk have this functionality and if so, could someone point me
to some examples??

Regs.

Iain.