yes, but it depends on what you mean by work. it will physically be able to work eg. call and text but im pretty sure the US sim cards will not work in UK's phones.
Firstly, enter 00 (or + by holding Down *). Then enter the countries dialling code (America's is 1) then enter the number as normal. For example - 408 487-6545 would be 001 4084876545.
Dial it as you would a normal UK number.If you are calling from the UK, dial the 11 digit number (e.g. 07123 456789)If you are calling from anywhere else in the world, use the UK country code +44...