[Bossman]

Even though the UK prepaid sim cards are one of the cheapest and the most discussed discussed here, it changes quite often. My suggestion would be to visit the respective carriers pages (Orange, Tmobile, Vodafone etc.) and compare them. One thing is certain, almost all of them have quite cheap rates to call the US, and the data rates to use them within the UK are quite good too.

I am sure the UK based members will be able to give advice as well.