Several users have reported an issue in which Bluetooth devices that worked well with previous iPhone models delivered muffled or muddy sound when paired with the iPhone 4. Users experiencing this issue report that people on the other end of phone calls say the iPhone 4 caller sounds as if he is “in a tunnel” or “underwater.” Other users report static, popping or otherwise poor audio quality.
Users have reported this issue with Bluetooth headsets from Jawbone, Motorola, Plantronics and others, as well as several car-based Bluetooth systems.
It appears that, in some cases, the issue is caused by the iPhone 4 inadvertently using its built-in microphone for outgoing audio, but the Bluetooth earpiece for incoming audio.
Some users report success with one of the “4 Rs” of iPhone problem solving laid out in our iPhone 4 troubleshooting guide; specifically, restoring, but not from backup.
It appears that bad holdover data from iPhone backups (especially those created for previous iPhone models) can cause various issues. Restoring as a new phone will delete contacts and other data, but may resolve the problem. To do so, connect your iPhone or iPod touch to your computer, click “Restore” in iTunes, then choose “setup as new phone.”
Super Reset. For Jawbone devices, a “super reset” may resolve the issue. Follow these steps, from Jawbone’s technical support department:
“1. Press and hold down the Talk Button on the Jawbone.
2. Connect the Jawbone to the USB charger cable. (The cable needs to be plugged into an active USB port or to an electrical outlet via the Wall Charger unit.)
3. Release the Talk Button.
4. Disconnect the Jawbone from the USB charger cable.
Turn on the Jawbone. It should begin to flash red every six seconds when it is turned on. While it is flashing red press the following sequence of buttons.
NoiseAssassin Button, Talk Button, Talk Button, NoiseAssassin Button, Talk Button, Talk Button
The Jawbone should flash red/white/red/white showing that it is in a manual pairing mode. Pairing mode will last for three minutes or until pairing is complete.
1. Set the mobile phone to search for all available Bluetooth devices.
2. When the search is complete, select “Jawbone” from the list of devices shown.
3. Enter the passkey (0000) and press OK to pair the Jawbone with your mobile phone. (When the pairing is completed, the Jawbone will beep and the LED indicator light will rapidly flash white eight times.)
(Note: For the passkey, please be sure to enter four zeroes, not the letter “O”.) 4. If prompted by the phone to connect, select “Yes” (this will vary between phones).”