If your iPhone is rebooting endlessly from iTunes 7.4 this *might* help.
This is for use with iTunes 7.4 and Mac OS X ONLY!
Please digg this to help others find this solution.
It may be best to reboot your Mac before performing the steps below:
Make sure you have at least iTunes 7.4 installed, then simply download and install the new 3.1 version of AppTapp Installer.
Make sure iTunes and iTunesHelper isn't running.
Download this.
Unzip it.
Run this command:
./iphonecomm -s 4
If it does work you can go ahead and run AppTapp 3.0
Next time be patient let us brick our phones when there is an iTunes update.