Vowlan -plz HELP

Hai i am new member to this group
I had a plan of implementing VoWlan .i am taking linux as my OS,

and wanted to code the application layer modules and rtp modules .

so if any body having intrest in the same field can help me out ..i wil
explain u everything in detail ..


thanks and regards .....

i would like to know which codecs are available for application layer
..and that should be licesence free..