Maybe this will help:
If you have a look at the VoipBuster FAQ # 48 here (and maybe others):
http://www.voipbuster.com/en/faq.html#8 there are some offerings of solutions for Mac and Linux users, which point to free Linux softphone (LinPhone voip) software stuff here:
http://www.linphone.org/
I'm not sure if porting of anything is required, but then again, I don't use this type of software so probably don't know much about it based on the brief reading I did before this posting. But, if you wanted to contact VoipBuster, they offer a Feedback link on their website.