Now you shouldn't lose anything during an OS update, before the desktop manager updaes the OS it created a backup and restores it when finished.
Just to be on the safe I usually do a manual backup before I perform the OS update just to be on the safe side.
Note: If you have any 3rd party software you will have to re-enter the registration codes again.
8830 -> 8330 -> 9550 -> 9650
Just think about how far BlackBerries have come from then till now... And what else is coming.
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