If your ISDN provider is AT&T or Sprint (the only 2 ISDN PRI providers, that work with ISDN calls over their network as 64K data calls), yes, you are supposed to register the DID's being used with them, so they can gurantee the calls will be routed as 64K data calls, as most Long Distance calls are handled as 56K voice calls. AT&T and Sprint are pretty much the only 2 companies in the US that can transit those calls as 64K data calls on their Long Distance networks. Yuo will discover this soon, if you havn't already. The symptom will be, other Video Conference units will be able to call and connect to you, but you will not be able to call them back, the culprit will be the LD provider is not handling the call as a 64K data call.
Mitch
AVAYA Certified Expert