So, I am visiting the uk soon and I wanted to be able to use my iPhone 4S. My question is if I order a micro SIM card now and stick it in my iPhone, will it be deactivated by the time I reach the uk and how long can I keep a SIM card in the phone before it needs to be topped up? So when I put the sim card into my iPhone will it show a signal and I be able to call 611 to top up or will making that call be impossible until I actually have paid for a top up voucher. Hopefully I won't have to buy a top-up until I'm actually in the uk. Which network allows me to use a SIM card in the phone to call to top up without expiring for a while is my question I guess. Thanks!