Ekiga is great, and ekiga.net SIP address is also great. What I really miss is an official windows build. It just takes too long, when the stuff I found via Google where working fine about 2 months ago. Also there is no such word as 'informations' in english. I understand that many french do this mistake (also others) but I do not like seeing it in ekiga.org website at all. It looks just bad imHHHHo.
Of course the fact that it does SIP great remains. I was able to use VOIPBuster service using Ekiga/Sip and it was an overwhelming experience and a very easy one.