The Preferred Roaming List (PRL) is a database residing in a wireless (primarily CDMA) device, such as a cellphone, that contains information used during the system selection and acquisition process.
PRL files can also be used to identify home networks along with roaming partners, thus making the PRL an actual list that determines the total coverage of the subscriber, both home and roaming coverage.
Many operators provide the ability for the user to download the latest PRL to their device by dialing an Over-the-air (OTA) feature code.
In the United States, for Verizon / MetroPCS / US Cellular, this feature code is *228 (*ACT).
For Sprint, it is ##873283# (it is also possible to use code ##72786# on Android or ##25327# on iOS to completely clear out the service programming and redo OTA activation, which includes updating the PRL).