I think Linphone used to have a CLI interface, so you might want to look
into it. I haven't used it in a long time, so I don't know what is its
current status. I basically gave up on SIP (partly because of very
spotty support for encrypted communications and for async messages like
SMS) and recommend Mumble, Matrix, or Jitsi for discussions over IP
instead; tho none of those support the "call" feature, so they require
some previous arrangement about when the communication will take
place :-( (Matrix trie(s|d) to provide that, but it doesn't really work
for me).
Stefan
