Most carriers lock your subsidized phone so you can’t use a 3rd party SIM card with it. This is inconvenient if you want to buy a cheap SIM card in a foreign country. AT&T says they will unlock your phone, but only under certain conditions. I’ve tried before and it’s a waste of time. I gave up and used HangUnlock. It cost $2 and took less than a day. — MF

PhoneClaudia Dawson