The four main mobile phone carriers in the United States: T-Mobile, Verizon, AT&T and Sprint, allow customers to activate their phones online. Some plans require an activation charge, but customers generally pay this when they sign up for the plan, not when they activate the phone.
For AT&T and T-Mobile plans, users enter a number based on the SIM card number, which the phone can sometimes detect automatically. Verizon and Sprint don't support GSM networks and don't use SIM cards, so users enter the phone's ID number, which is generally printed on the phone's box. Dialing a special phone number might also reveal this number if the phone is compatible with the provider's network.
In some cases, users need to dial a certain number of the phone to activate the plan even if they use online activation, so instructions sometimes ask the customer to charge the phone before activating it. In addition, it takes some time for the phone to register on the network, thus keeping the phone turned on can expedite this process. When bringing a third-party phone to a new provider, users might have to enter network names or numbers manually to receive text and image messages. However, phones branded with the provider generally connect to the right networks automatically.