A non-standard codec

Dear sirs, In the document RTP Profile for Audio and Video Conferences with Minimal Control There are description for several codecs, among them, GSM. But in H323 Version1/ V245 Version 2, there is no way to choose this codec. ¿Is there any way to work withs RTP "standard" codecs but H323-NON-standard codecs. Thanks a lot, Juan C Uribe G