I have been using iaxComm to access my iax2 service VoipJet.com.
LH can basically connect and make calls, but DTMFs don't work right inless I'm using headphones, suggesting the program is too simplistic to employ echo-cancellation. When at an automated prompt, for instance, pressing "3" results in the other end hearing "333".
Back to iaxComm for now.
LoudHush
IAX softphone for the Asterisk PBX.
Version: 1.3.21