Anecdotal evidence suggests that recent beta released of iOS 4.1 resolve 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.
Reader reports from users who have installed the latest betas of iOS 4.1 (which is currently available only to developers) indicate that this issue is resolved for many of the aforementioned Bluetooth devices.
Until the new release is publicly available, you can try the fixes listed in our previous post.