I noticed that my new Jawbone Icon works terribly with my iPhone 4. With the Bluetooth headset in my ear and the i4 in my pocket (less than three feet apart) the devices constantly un-pair and re-pair. The heads plays a "sonar" sound effect each time it happens. This didn't happen with my Jawbone Prime (the previous model), and both Jawbones work perfectly -- almost 30 feet away -- from my DroidX.
The iPhone 4 Bluetooth issue is more than just a few anecdotal reports, it appears to be more widespread. A number of people have reported issues, including users on Howard Forums and the Jawbone, Apple, MacRumors and EverythingiCafe forums. Everything points to a problem with the Bluetooth stack in iOS 4 on the iPhone 4 and hopefully this will be addressed in the forthcoming iOS 4 update.
Aliph, manufacturer of the Jawbone, acknowledged the issue to me in a statement:
We are aware of and concerned with the user frustration surrounding the issues affecting all Bluetooth devices (headsets, car kits, and speakers) connecting to the iPhone 4 and iOS4 updated phones. We know users have come to expect the freedom of hands-free and we are working night and day with our partners, Apple and AT&T, to resolve the issues as quickly as possible.
Apple hasn't yet acknowledged the problem or provided a timeline for a fix.
I'm guessing that July 24 would be the drop-dead date for Apple to release iOS 4.0.1. Otherwise iPhone 4 customers may begin returning their phones en masse before Apple's 30-day, no-fee return window closes.
Mine is going in to the Genius Bar today.
Update: I tested my Icon headset with another iPhone here at The Apple Store and it worked fine. I walked about 30 feet away and it held the call) -- mine barely makes it three feet, so they're replacing my iPhone 4 with a new model. The replacement iPhone 4 service item, as opposed to the retail package, comes in a black padded return shipping box with no accessories.
Update 2: So far so good on the Bluetooth front. In the first four hours of testing. I've been able to keep a reliable connection between the Jawbone Icon headset and the new iPhone 4 while carrying it in my pocket. I've also been able to get 30+ feet of range between the i4 and the Icon headset in an outdoor setting. The picture below is me (wearing the white shirt) almost 40 feet from the new iPhone 4 and the BT connection was perfect. Bluetooth was definitely a problem in my iPhone 4, but it may not be with every iPhone 4. Obviously, your mileage may vary.