If you're looking to use a Boost Mobile phone, you'll need to make sure that it's compatible with the carrier. In general, most Boost Mobile phones will work with other carriers, but there are some exceptions. For example, the iPhone 5s is not compatible with Sprint or Verizon.
To find out if your phone is compatible with another carrier, you'll need to check the specifications of your device. Most manufacturers will list the carrier compatibility on their website. If you can't find this information, you can also contact customer support for help.