I am on iOS 5 unteathered JB on my old bootrom 3GS and I went to the Software Update on Settings to check the change log for it.
I saw that it was downloading automatically and I quickly switched the phone off. I did not press "Download and Install" I just saw it say 1 minute remaining of the download.
I switched it back on and hooked it up to iTunes and told it not to remind me of updates.
Is this the method to stop automatic updates on iOS 5?