*** UPDATE 23/6/09 – While callwithus still have a UK sip server you should use the server ‘sip.callwithus.com’ in your configuration settings. Check the callwithus website for details.
If you’re based in the UK or Europe and looking for a cheap ITSP (VIOP provider) it might be worth looking at CallWithUS as they’ve recently launched a UK based SIP server.
As well as the US based servers sip.callwithus.com, east.callwithus.com and west.callwithus.com you can now use uk.callwithus.com. I now get sub 6ms pings from my Asterisk server in BlueSquare to the CallWithUs server.
I’ve been using CallWithUs for a while now and they provide very competitively priced DIDs and termination rates.