I have a server from Alliance systems which is the I 5000 with 2 (two) D480 Dialogic dual T1 cards. (only one is used)
The server intercepts calls sent from a Nortel Norstar telephone T1 card and verifies the digits sent against the National Do Not Call List. The list is held in a separate SQL server that returns a 1 or zero to the Alliance server depending on if it is a listed phone number on the Do Not Call List. If it is not on the list the server connects the call to the carrier T1 for completion. This is a simple number look up that either accepts (connects the call by sending digits to the carrier and conferencing the inbound Nortel channel with the outbound carrier channel) or rejects the call and sends an error tone back to the open Norstar channel.
The T1 interface from Norstar is D4 AMI SF as is the same to the carrier.