Can I put a prepaid US SIM card in my iPhone 5? I am visiting the USA later this year and want to use my (unlocked) iPhone 5 for calls within the USA. I'll need to use it on arrival. Can I buy a prepaid SIM card online and have it shipped to the UK so that I can use it straight away? John Van der Vord, by email Yes you can and there are plenty of sellers on ebay and Amazon, both in the UK and US, with prices starting at around £5.00, but it can be a bit of a minefield. There are a number of technical issues concerning which version of the iPhone 5 you have, and how it was unlocked and these can determine which networks you can use and whether or not some features or apps will work. There is also the question of network coverage but providing you are not going too far off the beaten track the safest option for most iPhone users is a pre-paid SIM card from AT&T. It is the USA's second largest provider and airtime vouchers are very widely available from retail outlets. However, whichever network you decide to use there are a few things to be aware of. Some US SIM card deals require hefty up-front payments for airtime, which you may not want or need if you are only visiting for a short time. Check the tariffs carefully especially if you expect to make or receive calls or texts from the UK or make use of your phone's data or mobile broadband facilities. Make sure you read and understand what is involved in activating the card online and how you go about buying credit or top-up vouchers when you are there. The setup for some cards can be fiendishly complicated, and you may not be able to test if it is working until you arrive in the US. Print out the instructions and any numbers you may need to call if you encounter problems. Aim to activate the card a week or so before you leave and this will give you plenty of time to give your new phone number to anyone who may need it and finally, get used to calling your mobile phone a "cell,"