The LDID option of SDRR allows you to apply a DMI and terminate the call internally, rather than routing the call according to the RLI the NPA, NXX, or SPN you have dialed points to. I believe the LDID feature is intended to avoid users occupying both an outgoing and incoming trunk for an internal call. That is, if I wish to call my colleague in the same PBX (DN 1234), but I dial 9+555-1234, NXX 555 would be programmed with LDID 1234 to recognize this number as a internal DID DN, and strip off the 3-digit NXX via a DMI. If all the 1XXX DNs are valid DIDs in my PBX, then NXX 555 would have LDID 1. You can also use LDDD to recognize a 'main number', and use a different DMI, say to strip off all dialed digits and insert '0' for the Attendant Console or other internal DN. Similar prog. can be added to 10-Digit NPA dialing (e.g. 9+555-555-1XXX = DIDs: NPA 555 LDID 5551, DMI to delete 6 digits), to prevent unnecessary trunk utilization.