Are we sure that this is a standard UK mobile number rather than some premium rate number, e.g. an 0702 or an 0900 number os something. Also, note that many of those funky UK numbers cannot be called from outside the UK at any rate.
With respect to the US rates, checkout this link:
http://0044.co.uk/global-sim-coverage.htm
This is their coverage list. It says that the US is a country with incoming call charges.
Also note that incoming calls in Canada are US$0.59 a minute. Canada and the US are usually the same rate. What's the difference here?
Note: their rates for Russia aren't bad.