Can I use Bluetooth with the iPhone in airplane mode?
Yes, you can use Bluetooth with the cellular radio, GPS and Wi-Fi off. To enter airplane mode:
Navigate to Settings -> Airplane Mode -> ON
This turns off all radio activity including cellular antennas and Wi-Fi. Now while staying in airplane mode you can turn on Bluetooth only.
Navigate to Settings -> General -> Bluetooth -> Bluetooth ON
Your iPhone will now use the Bluetooth connection while keeping all other radios off.