I have these scenarios with different result
1- 1st scenario (Conference success)
IP Phones ----CUCM----SIP GW---PRI----PSTN
IP Phone A (Region A) has call with IP Phone B (Region B) using g729 codec for this call , then make conference with PSTN Number using codec g729 and conference success .
2- 2st scenario (Conference failed)
IP Phones ----CUCM----H323 GW-------Avaya PBX
IP Phone A (Region A) has call with IP Phone B (Region B) using g729 codec for this call , then make conference with Avaya Extension using codec g729 and conference failed
Please note that
Calls between any IP Phone and Avaya extension use g729 Codec.
All IP Phones has MRGL with conference bridge and transcoder
H323 VG between CUCM and Avaya has MTP required.
Phone A has call with PSTN number using Codec g729 then try to make conference with avaya extension but Conf failed.
Please check attached sdl FILES FOR third scenario
Phone A number is 6668
PSTN number is 01018868XXX
Avaya Extenstion 962