If you can not receive calls while your iPhone is "sleeping" and only while the screen is on. This may help. I have used this on 2G phones running 2.2 firmware ONLY. I do NOT know if it will work on a 3G. I can't imagine why but I don't want to imagine you messing up your phone. MAKE A BACKUP of these files. Use your favorite way to get into your phone
These 3 files go into
/System/Library/SystemConfiguration/PowerManagement.bundle/
Reboot your phone and then make a backup on iTunes. I have a feeling these files get replaced from iTunes last backup.
