Although the OP has asked the question on uk.telecom.voip, I cannot
help but suggest that the cheapest way to get an incoming number is to
blag an old & worthless mobile from a teen who has just shelled out for
the latest mobile equivalent of a new pair of trainers and then buy a
pre-pay SIM from Virgin or whoever. Sorry to be boring, but if anyone
can beat £10...

PS. When are you guys going to stop bickering about Sipgate. Why not
meet up, have a few beers and put it to rest?