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. In the case of -based CDMA devices, the PRL resides on the R-UIM. The PRL indicates which bands, sub bands, and service provider identifiers will be scanned and in what priority order. Without a PRL, the device may not be able to roam, i.e. obtain service outside of the home area. There may be cases where missing or corrupt PRLs can lead to a customer not having service at all. On many networks, regularly updating the PRL is advised if the subscriber uses the device outside the home area frequently, particularly if they do so in multiple different areas. This allows the phone to choose the best roaming carriers, particularly "roaming partners" with whom the home carrier has a cost-saving roaming agreement, rather than using non-affiliated carriers. 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. The PRL is built by an operator and is normally not accessible to the user. 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). In Canada, for Telus Mobility, the PRL update feature code is *22803 (*ACT03). PRL structure The PRL consists of two tables (along with some header and overhead information): Acquisition Table – An indexed list of frequencies on which the device may search for particular systems. The idea behind the acquisition table is to optimize the acquisition time by identifying only the frequencies that should be searched, rather than searching the entire frequency spectrum. The information contained in each acquisition table entry includes an index, the network type, and associated channel blocks. System Table – A prioritized list of systems that the device is permitted to access (Preferred Systems) and those that it is explicitly forbidden to access (Negative Systems).