I have been testing something similar with an Adtran 908 using sip extensions and a T1 E&M wink connection to a 3300. My setup's purpose is to test some T.38 faxing, but the principle should be the same. I have the DSX port from the Adtran connected to the PBX using D4/B8ZS. As my test setup is sitting in my basement at home, from memory I have the voice trunk group set to accept both 4 digit and 91XXXXXXXXXX. I have the DID digits set to pass the max 16. From an external sip ata, I can dial either an internal extension or likely back out another trunk(haven't test this, but calls complete to the internal extension and 9 plus seizes the tie an provides reorder as expected due to not having that peice build).