T-mobile roms use 'Google Services Framework' for the update, and obviously you can't freeze that app.
So, what you do is d/l a program called 'Autorun Manager'. Then inside that program, scroll down to 'Google Services Framework' and disable 1 receiver.
The one you want to disable is called 'com.google.gsf.update.SytemUpdateService$Receiver ' Just disable that (by unchecking it) and then reboot. You will not receive a notification to update ever again.
Also, go into the folder /cache and delete the FOTA d/l. You will need R/W permissions in the root directory to do this. So use whichever file manager you prefer for that.
The FOTA d/l is easy to spot, it's a 150mb approximately zip file with a bunch of chars and should be the only file in that directory. There are a few folders as well, but, ignore them and just delete the 1 file.