[kirstein]

To answer the noob questions,
PRL is Prefered Roaming List. It is a list of tower IDs that the phone is allowed to roam onto when it can't find a usable signal. The list gets updated regularly as new towers are built and new roaming agreements are negotiated. An an update may do nothing for you at all if there aren't any changes in your area. A really old list may cause some you to not be able to roam in some area or your phone may try to roam onto towers that Sprint has no current agreement.