iPhone mobile device with firmware OS version 2.0 (including iPhone 3G) will make a full image backup of the iPhone device with all installed applications, instead of just documents and library data to computer (Mac or PC) during the synchronization process, each and every time when there is a change to the installed apps and games
iPhone users have to manually cancel the backup in iTunes when iPhone backup process is in progress to skip and bypass the slow backing up of iPhone, but terminating the backup process halfway may result in corrupted backup,
he workaround is to use the following hack to force iTunes to disable backup process and skip backing up the complete iPhone image.
1. Quit iTunes.
2. Open Terminal.app.
3. Type (or copy and paste) the following command, and then hit Return:
_defaults write com.apple.iTunes DeviceBackupsDisabled -bool true_
4. Open and run iTunes.
5. Plug in and connect iPhone 3G or original classic iPhone on version 2.0 OS to computer for syncing. The backup process should be bypassed and skipped now, and only music or podcasts are synced.