Your phone must use SIM cards (not CDMA only)
Your phone must be unlocked (i.e. not programmed to only work with your original carrier’s network)
Your phone must be a 3G (UMTS/HSDPA) phone, operating on a minimum 3G band B1(2100), with B8(900) increasing 3G coverage.
In order to take advantage of 4G speeds, your phone must be operating on 4G band B3(1800), with more 4G frequencies from the below chart increasing 4G coverage.
Confused? Try this: Go to your phone manual or an online site (we recommend GSM Arena), and look up your phone model.