software modem with IAX2 connectivity

 IAXmodem is a software modem written in C that uses an IAX channel (commonly
 provided by an Asterisk PBX system) instead of a traditional phone line and
 uses a DSP library instead of DSP hardware chipsets.
 .
 IAXmodem was originally conceived to function as a fax modem usable with
 HylaFAX, and it does that well. However IAXmodem also has been known to
 function with mgetty+sendfax and efax.