While iOS 4 is delivering on every promise for the iPhone 3GS users out there, as we were all told up front, the iPhone 3G would be missing some of those touted new features. Granted, we knew such disparities would exist but were never given the finer details. Now that the final build is percolating through the internet, we decided to take a look at what features are and aren't working on the earlier year's model.

What's there
Folders
Threaded mail
iTunes playlist creation / editing
5x digital zoom: just tap on the display near the capture button, but be warned, it doesn't paint a pretty picture
iBooks: we were having issues with the earlier build, but it seems to be running fine after today's official download -- PDFs work, too.
Photos: you can now sort by albums, events, faces, and places
Game Center: the icon is present, but as of this writing we're unable to connect to the servers. (Update: a number of readers saying it didn't come with today's download. We nabbed ours as a gold build, which might explain the discrepancy despite still being considered "up to date" by iTunes.)
Spell check has been updated
Spotlight search: you can search the web and Wikipedia from the home screen search bar. That said, not all our queries -- "Engadget," for example -- weren't offering the option. [Thanks, jkane08]
What isn't
Multitasking: this is the big one. Double-tapping the home button doesn't give you the handy menu, there's no fast app switching, and background use is missing in action.
Screen lock: normally in the multitasking menu (which isn't available on 3G), it's nowhere to be found, even under Settings. Bummer.
Home screen wallpaper: you'd think this simple addition would make the cut, but sadly no. The dock has been given a visual upgrade, though.
Bluetooth Keyboard support: we haven't tried this ourselves, but an influx of reports from Twitter suggest this is also a no-go.

http://www.engadget.com/2010/06/21/i...er-multitaski/