"Update PRL" makes the same type of request to the OMADM, in this case though it sends your Preferred Roaming List.
This is basically a list of tower Ids and capabilities.
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. There may be cases where missing or corrupt PRLs can lead to a customer not having service at all.
When you select "Update Profile", your device connects to sprints data network and makes a request to the OMADM (open mobile alliance device manager), which in turn pushes a prov XML file to your phone with your MDN, MSID, username, primary and secondary HA ip addresses, HA password and AAA password.
There are probably a handful of other values involving wimax and such but I don't know what they are.
This information can include your phone number, or be related to the roaming network, the sign in credentials that are needed for you to access the internet, and more.
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.
Follow any required prompts (if any) to complete the file download and installation.
Press the "end call" button when the phone prompts you.