The below method is not yet tested with iOS 4.0, if you try it, please post a comment if it works.

Most iPhone OS 2.0 / iPhone 3G users have experienced the very slow backup process each time the iPhone is connected to iTunes, and as more applications are installed the process will take even longer. It is possible to just cancel the backup process, and then make a regular Sync without backing up. However, if you want avoid the backup process from starting, there is a workaround. It is possible disable the automatic backup process from starting, and how to do this is described below; firstly for Mac users, and secondly for Windows users:

Mac users:

1. Quit iTunes.
2. Open a Terminal (Applications > Utilities > Terminal)
3. Type or copy the following command:
   defaults write com.apple.iTunes AutomaticDeviceBackupsDisabled -bool true
4. Open iTunes.
5. Connect the iPhone.
6. Make Sync without backing up.

To enable automatic backup in iTunes again use this command instead:

Note: If you previously have used the command line option that entirely disables the backup feature, then type this command as well to enable to backup process:

Recommendation: If you choose to disable the automatic backup process, it would be a good idea to manually making a backup it once a while to get a safe copy of text messages, call log and like (just right-click your iPhone icon in iTunes).

Windows Users: (updated)

Windows users can use the same approach:

1. Quit iTunes.
2. Press Win+R (opens the Windows Run dialog)
3. Type or copy the following command:
   “%CommonProgramFiles%\Apple\Mobile Device Support\bin\defaults.exe” write com.apple.iTunes AutomaticDeviceBackupsDisabled -bool true
4. Open iTunes.
5. Connect the iPhone.
6. Make Sync without backing up.

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