I have a customer that has a PRI with incomming digits 0600 converted to 8100.
This is on a 500 set with MCR keys on about 12 3904 telephones. They can only get 2 to 3 calls before getting a busy.

We have the same senerio with DID numbers and they can receive several calls at once.

IS there anything that will limit the number of IDC calls.

I didn't think you could have a DN on a 500 set and make it MCR on other telephones... so I don't have an answer.

Have you tried the above scenario by removing the analog set out? I think once the call lands on the analog, further calls may busy out.