I want to buy a razr from craigslist, but I can only find at&t razrs. Will it work with my tmobile plan if I put the sim card in, or does it have to be unlocked first?
Yes. You need to unlock an AT&T phone to use it with a T-Mobile SIM card. You can get the unique unlock code for an AT&T network locked Razr from SuperUnlockCodes.com at affordable cost with an easy unlocking guide.