I'm looking for a SIP client on Linux which I could control through a pipe, or a high level library to incorporate one in my software. I tried Linphone, which is quite good, but seems to have some instabilities, as dropping sound when talking with an Asterisk server. I'm currently looking at OpalVoip, but I thought I'd ask to the experts... Thank you
This page lists just about all your options. sofia and sipx are used in popular VoIP applications so they are probably good bets.