This method only works on AT&T, T-Mobile, Verizon and Sprint Samsung Galaxy S3.
What is PRL means?
PRL stands for Preferred Roaming List. Its a list of roaming towers in your area. Its best to keep this updated in crappy coverage areas.
What is PRI means? In actuality it is called "Product Release Instructions"
and is essentially a list of settings for the radio. It's the PRI which uses the PRL to enable data roaming by connecting it to towers/cell sites listed in the PRL and for other things such as to allow calls to interrupt an active data session (ring-through).
http://forum.xda-developers.com/show...=751935&page=7 <- Debate on what it stands for. (REALLY?!)
How do I update my Samsung Galaxy S3 PRL/PRI?
Go to Menu > Settings > System Updates > Update PRL + Update Profile.
How to Manually Change Your PRL with DFS CDMA Tool (Sprint Samsung Galaxy S3)
There are various methods for doing this. I've seen various results as well. I know this might seem a little lengthy for some, but the knowledge you pick up using these other tools should prove to be helpful in the long run. These tools are powerful, and I've spent more of my time using them that flashing ROMs and other stuff since I mainly run a Cricket website.
The end result is your device having the PRL you want on it.
Samsung Galaxy S3 Drivers -
Support - Sprint Cell Phones SPH-L710 | Samsung Cell Phones
(Support > Manual & Downloads > Software)
DFS CDMATool (DEMO) -
CDMA Tool. DFS software. www.cdmatool.com
MSL - You can call Sprint or use a variety of methods to obtain it. One is in the video directly below.
Source: USgalaxys3.com, XDA-Developer