Inter-tel 5000 + Asterisk Integration sip or trunk

I have a inter-tel 5000 and I want to send some calls to my asterisk system.

I was wondering if its anyway possible to send calls over a sip end point on the inter-tell to the asterisk system?

Would a sip trunk between the two be an easy way to connect the two systems?

How would I trick inter-tel 5000 to think asterisk is a sip phone client?

Any ideas on this would be more than welcome

Asterisk 1.6.2 with ubuntu 8.04

Thank You.