I just obtained a US local number (area code 201 - New Jersey) and look forward to using it in the US shortly. I called the number from the UK and my cellphone rang, so it's just about up and running.

For £5 a year, I'll probably retain the number permanently. No need to bother with contracts.

Given the flexibility with up to 10 local numbers, this looks a good prospect for international roaming. Just one problem for me, they offer no service from South Africa, probably the only SIM card provider without such service.