Well, having fixed a few bugs, and then spent ages arguing with linux library calls this evening, we have all working well with VoIP.
The sky box was fun - or rather the supura not the sky box was the issue. Simple missing check in my code.
What is interesting is that modems and faxes over SIP are apparently bad. Well, so they say.
But SIP is providing full a-law 8,000 samples per second the same as ISDN. So, well, it should just work. But the world of SIP users and carriers have it drummed in to their head that fax and modems do not work.
Well, now we have our own call sever and no asterisk, we have SIP working better.. My Sky box will go on line and access my sky account... over SIP... woohoo.
All good fun.