Since we have a developer account on Apple.com, we downloaded OS 4 firmware for my iPhone 3GS:
I setup my private Gmail account and the Lotus Traveler account for my Lotus Notes mailbox.
Later I will test all new features (multi-tasking, folders, etc.)
Note: installing the new firmware requires to download the new iTunes 9.2 beta available ONLY for Mac.
The firmware itself is available in .dmg file format.