VoIP/SIP client

Hi all,

Sorry if that kind of general question is not suitable for the list, in that case just forget it!
Here is my question:
I am trying to work out a lightweight SIP client for my board, has anybody of you guys already done that and what client would you advise? It seems that there are a couple of interesting libraries for VoIP applications already available in buildroot (i.e. speex, libosip2, libexosip2), but don't see any client, am I wrong?

Kind regards,

Emmanuel.