AXEY:
I highly suggest IDT GLOBAL CALL CARD, a prepaid card- $25 minimum. They advertise in airline magazines and I recently used them extensively to call from the UK back to the US. To activate call 1-800-299-2534

Sample rates would be:
From USA, per minute +15c/call
USA 8c; Canada 10c; Germany 12c; Japan 15c; UK 10c.

Back to USA:
From UK-10c
From other places - much higher.
You can access a toll free UK# from most phone booths 0800-279-3325. Very good operation.