The Model 4596 lets you use AT&T 3G service without making an expensive long-term commitment. In the U.S., sign up for service wherever AT&T mobile broadband is sold. A voice service or another account with AT&T is not required. The modem is activated by plugging in a standard SIM card from AT&T or another GSM service provider. Unlike other modems, the Model 4596 is not locked to a specific service provider and can use a data SIM from services around the world. A change to the service provider is accomplished by simply sliding out one provider"s SIM and replacing it with another provider"s SIM. It takes only seconds and maximizes flexibility in using data plans.