I was looking for a small, lite weight software based phone for my Windows laptop that would connect back to my Asterisk PBX using the IAX protocol. iaxLite is perfect and works great. I haven’t tried sipLite (same phone but uses theSIP protocol) yet. Well worth a look if you are using Windows.
Soft Phone : iaxTalk.com !, VOIP::Asterisk::Phone::ATA::USB

iaxLite is a IAX2 softphone. sipLite is a SIP softphone