It updates any new towers or updates the existing towers with any changes. Yes Crickee it also does tell it where to search. But for watkins and vstro if this keeps happening. Go into manage connections and turn off your network, pull the battery for bout 60 seconds, let the phone boot up, go back to manage connections and turn you network back on. You can pull your battery like I do or you don't have to. Wont affect anything I just have that habit

Also when you update your PRL make sure to do a battery pull after

Hope this helps as sometimes it can be the radio, network, or even the phone (<not likely)