Here`s how to switch to a new carrier
(Android Central)

Best answer: If you want to keep your phone, it will need to be unlocked and compatible with a new carrier. To keep your number, you will need to port with the new carrier. Be sure not to cancel your old account until your port is complete. Which carrier should you switch to? One of the main things to consider is the network. While all carriers have made huge strides in recent years to make sure they offer service where most Americans live, some rural areas still strongly favor one carrier. Check out the coverage maps for AT&T, T-Mobile, and Verizon to get an idea. If you like the network but don`t like the plans, it`s time to check out an MVNO. The best MVNOs can save you money by getting rid of the features and services you don`t need and offering a simplified phone plan. For example, if you know you need the Verizon or T-Mobile network, you can choose an MVNO based on Verizon or an MVNO on T-Mobile. Unless you own money on it, you can probably bring your phone as well. ...