[Freeswitch-users] frame per packet

Hi, I'm building a voip client for android phones over gsm and consider using FS as sever. In order to save cellular costs I want to put more than one frame per Rtp packet. Is there any easy solution to do it in FS? Or, where is the right place to add it? In mod_sofia or sofia_glue? should I go to lower levels? I don't think I should do it in the codec, it may cause problems in the rtp sequence number and probably a lot more. TNX, Ken