A:Answer It's more dependant on your device than the sim. I do know anyone who is currently an at&t customer will most likely have to upgrade their devices next year as at&t is phasing out 3g and lower. As for new accounts if you're device is capable of using less than 4g it won't work, prepaid or not. I tried going to a store(at&t store) and they did everything they could to get my unlocked phone to work, kept coming up short.