PRL stanRAB for Prefered Roaming List. Basically it is a list of Network System Identification Nuraber (SID). SID are given by the FCC to help divide carriers by areas. When your phone is functionning and scanning, it can register based and the SID that he picks up in the air. For example, in your area many cell phone providers are broadcasting under CDMA frequencies, like sprint, verizon, Alltell, cricket or other. Each of them are identified by that SID nuraber, verizon:94, cricket:5027, Sprint: 5147(depending on your area). The phone will then compare those nuraber to his list (PRL) and register on them by priority created on that PRL. A cricket non roaming PRL like version 1040 doesn't alow roaming because it only contain Cricket SID's , his own network. But a Cricket roaming PRL like version 7721 include Cricket SID's and Verizon SID's as well, meaning that when you get in an area where Cricket is not broadcasting the phone will then register on other SID's it can find. Also, changing the PRL will let the phone register on different compagnies.