If you are regularly in the UK and dealing with UK people who will want to call you on a UK number, you should consider getting a regular contract with Three. The normal contract includes Feel at Home which counts all calls received in the USA on that SIM, and all calls to the UK on that SIM whilst in the USA as included minutes. This effectively gives you a UK number to receive calls foc for your contacts to use, as well as an ability to make free calls to the UK foc - particularly valuable to mobile numbers which would otherwise be very expensive.