Hi.
I update (not restore) then use redsnow to jailbreak and activate. All of the information (inclide Mail, contact, calender data, my appps, my musics, picts...) remain on the iPhone. It sure does not clean the iPhone if you chose UPDATE in iTunes.
In case update does not work, you can RESTORE your iPhone to OS 3.0 BUT you need to back up your data to iTunes before restoring your device. After restore and jailbreak, you can use iTunes to restore your data back to your iPhone.
In any cases, be sure to back up!!!