Possibly a little OT.....
I use sipgate for incoming (nice 0845 number) and voipfone for outgoing.
http://www.voipfone.co.uk
I have purchased an inner London number and grabbed a nice Cat5 Ethernet phone from e-bay. Now I can answer my 'office' number from the comfort of my front room
I can also take the phone with me to work and plug it in there.
Voipfone are a bit cheaper than sipgate and a LOT more reliable. (my sipgate account was a bit poo for making calls, noticeable delay was the worst part)