I deleted a system file on my iPhone 3G that disabled Bluetooth. How can I restore it?

The most effective way to recover missing system files on an iPhone 3G is to perform a full restore using iTunes. This process will reinstall the operating system and restore all factory files. Before proceeding, connect your iPhone to your computer and create a backup to ensure your messages, photos, and other data are safe. Once the restore is complete, you can reload your backup. If your device was jailbroken, you will need to re-run your jailbreak utility after the restore to regain root access.