http://tinyurl.com/qz2p52x
All that Freedompop's UK site does is take your address details and say that they'll contact you when the service is available, but it does appear to be genuine if eBuyer aren't lying.
later - reviews of their US service say it's a bit slow, with coverage poor and no technical support unless you pay for it. Might still be worth considering for very occasional use, but only if I can find a suitable unlocked phone cheap.