My Client has just aquired a 3 branch company who currently has 3 Intertel Axxess connected together via PP T-1s. They also have a complete spare system which they would like to move to their HQ location to provide connectivity to the Tadiran PBX via direct T-1/E&M. The connection will be provided over AT&Ts MPLS EVPN network, so a Cisco Router at each end will provide the T-1 connection. I understand that Inter-Tel uses a proprietary PRI D channel format to connect two systems via T-1, so the Cisco Routers will not support the proprietary D Channel.

Any suggestions?

You are correct in that Inter-Tel can not use the D-Channel. You would have to program the trunks as E&M, connect them to an Axxess T-1 Card w/o PRI enabled. There would be no feature transparency, no centralized VM only simple dial tone between sites.

That would mean the it would not make sense to move the spare unit to the HQ location, just provision E&M tie lines between the Axxess and the Tadiran. This will also eliminate the Loop Release feature if calls were transfered back to the Axxess, that would use two paths and conversion twice from TDM to VOIP.

Is there a VOIP solution that would work between the two Axxess that would provide for loop release?