From apple insider:
Users of iOS 4 on both the iPhone 4 and iPhone 3GS say their handset has constantly dropped wireless Bluetooth connections with both headsets and in-car systems.
Numerous users contacted AppleInsider to say that they have experienced a number of problems specific to iOS 4 with Bluetooth connectivity. A number of people who upgraded their iPhone 3GS found that their phone’s Bluetooth became problematic, even though it worked fine before the iOS 4 update. And others who bought a new iPhone 4 have encountered some of the same issues.
“Nearly every time I’m in my car the iPhone disconnects from the built-in Bluetooth system,” one reader with an iPhone 4 wrote. “This never, ever happened with my 3G phone. I have a case number with AppleCare and they refuse to acknowledge the problem or replace the phone, even after having the problem persist after downloading a fresh copy of IOS 4, reinstalling the software and setting the phone up bare with no other apps. Could this be another antenna problem?”
In numerous threads on the official Apple Discussions forums, users have shared similar problems (1, 2, 3, 4). Those threads have only grown since iOS 4 and the iPhone 4 were released in late June.
Users have said that their Bluetooth connections will sporadically drop after the two devices are successfully paired. Others can connect, but are met with a message that says “no media found” when trying to play music. And some said they have experienced muffled voices when placing a call over Bluetooth.
Some users on the forums noted that the recent iOS 4.0.1 update did not fix the Bluetooth issues. The minor update featured a cosmetic fix that changed how the iPhone reports bars of signal strength.
The Bluetooth pairing issues are said to exist across a range of devices, including vehicles from Mercedes-Benz and BMW, car stereos from Pioneer and Alpine, and headsets from Motorola and Jawbone.
Some said they have fixed the problem by resetting the phone’s settings. This can be done by launching the Settings application, choosing General, Reset, and Reset All Settings. Interestingly, the same fix was said to work for some who experienced issues with the proximity sensor on the iPhone 4. Apple has said it is working on a software fix for the proximity sensor problems with the iPhone 4, but has made no mention of the reported Bluetooth problems.