Receive call from multiple SIP accounts using one client.
Finally found a decent free, no hidden costs, and open source VOIP multi line line client Linphone.
It works rather well, doesn't look like dogs breakfast, hasn't crashed yet, and best of all it's also a multi platform client - it will run on your Blackberry, Android, iPhone, Windows and Linux. So in a nut shell if you have multiple sip accounts or run your own PBX system like FreeSWITCH it does the job, and it does it well.
Yes you can thank me, but real thanks should go to Yasuro's Blog, I just got legendary googlefu.