I didn't get any response to my query about implementing a modem on freeswitch so I thought I would try to write one.
Excuse my ignorance/naivety but can anyone point me in the right direction for writing a module that can receive the RTP frames and decode them using my tone detection algorithm. and for taking my data and sending it back out via RTP frames/packets. 
Could I take an existing module, and use that as a template, I'm a good C coder but might struggle to start from scratch with FS in my timescales.
Any thoughts on where best to start this?

All the best,
Paul Collister paul@collisters.com