Unlocked- will work with GSM carriers in the USA and internationally. In the USA it will work with mobile networks including T-mobile and At&t as well as smaller companies which are using their towers including Simple Mobile, Lyca Mobile, Ultra Mobile, H2O. You must have your own sim card or purchase a new sim card. Verizon-Will only work with Verizon network and you must have your own sim card. Sprint- Will only work with Sprint network and you must have your won sim card.