Okay...it came up again and here's exactly what the message says word for word. This message pops up randomly every few minutes.
A system update is ready to install. Your Android device will restart and install the update. You will not be able to make any calls, including emergency calls, during installation.
Install later More info... Install now"
"Install later More info... Install now" are the choices available. Clicking the back button is the same as "Install later", I believe, as it just postpones the message until later.
"More info..." brings up another dialogue saying:
"Android system update
This Software Update includes new enhancements and improvements for your Samsung Galaxy S III. You will be unable to use your device for the duration of the install, which is expected to take several minutes.
Restart & install"
"Restart & install" is my only option other than clicking the back button which works just as before where it just postpones the message until later.
The message is getting annoying and I'd just like it to go away because I have no want to update. I am not interested in flashing third party ROMs either because I'd like to get to continue using the stock ROM with root privileges for the time being.