[AT&T, Rogers, Bell, Telus Samsung Galaxy S III] cozanostra:
This is to confirm that I managed to install the most recent OTA JB leak from my out-of-the-box Bell Galaxy S3, without having to flash anything, no CWR, no rooting required. Also didn't have to wipe any data or factory reset, after the update all my apps and data were in order as if I did a Kies update.

This is all you need to do - keep in mind this only works for

UNROOTED

stock Bell firmare (I747MVLALH) cannot by any means guarantee results for any other carrier/version.

Download latest OTA leak here

Save zip file to EXTERNAL SD CARD of your phone, do not unzip or rename.

Boot phone in stock recovery (Turn off phone & start up by holding down Volume Up+Home+Power, let go when the Samsung logo appears)

From Recovery menu select ->Wipe cache partition (this step, if ignored may be the reason why this didn't work for other users)

From Recovery menu select ->Apply update from external storage->select zip file you saved on external SD earlier and let the phone do its thing. It will take a few minutes before the slider bar shows up so don't panic thinking that its not working, in my case the upgrading process took about 15min

Restart phone, and enjoy JB!

All apps and data were still there, no need to reconfigure anything. Flash counter did not get tripped, ROM still shows as "Samsung Official".

Bell TV app still works, which means that Bell still recognizes the phone, however KIES does not, so for upcoming official OTA update you will need to revert back to stock ROM.

Google Now works great, the speech recognition is almost flawless, has recognized everything I said and I have a pretty thick accent in English. To get it working, you just need to update Google Voice search, for me the update request showed up automatically.

As far as bugs, only thing I found so far is WiFi tethering will only work when set as open (no password) and grey notifications bar (which may be just part of design). Some people reported issues with music player but its working fine for me.

As for performance, I find that apps open with zero lag, I did find some choppiness when scrolling lists in certain applications and websites. See attached quadrant result.

For those who try it please post experience and other issues/bugs that may be there.

Update: To enable voice response from Google Now, download this from Play Store, then select US English language, thats it!(credits to DEEZENUTSZ)

Update: some users reported GPS inaccuracies, this can be resolved by clearing cache data for the maps application. Mine works great so far.

Update: ***IMPORTANT PLS READ*** All app related issues reported by users in this thread (GPS, maps, bluetooth, music player etc) are resolved by clearing cache and data for each app. Alternatively, you can do a factory reset and it will take care of every app issue and force closes. Again, the above method works only for STOCK UNROOTED Bell ROM, any other ROM would require ODIN flashing and/or flashing stock Bell ROM first. I will no longer reply to issues that have already been discussed, so before you start firing your negativity bombs, please take the time to carefully read this step-by=step guide and all the updates I added. Oh, and don't forget to thank me once in a while :D