Informal testing here at TUAW central with a couple of Jawbone units on both an iPhone 3GS as well as the iPhone 4 showed that the 3GS displayed none of the problems that the iPhone 4 is demonstrating.
It turns out that problem is not isolated to the unit I tested, let alone the manufacturer. At Apple's discussion forums, other Bluetooth headsets are apparently producing the same distortion effects when used with many iPhone 4 units.
An iPhone 4 antenna glitch may lie at the heart of this matter. A spokesperson for Aliph states, "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."
This appears to be another strike against what is clearly a troubled device.