A number of readers have reported a problem where having Wi-Fi active on the iPhone results in interference with Bluetooth activity, particularly when attempting to use Bluetooth connectivity with car integration systems.
The interference generally results in a breaking of the Bluetooth connection, or distorted audio on phone calls, and can be resolved by simply turning WiFi off on the iPhone (Select Settings then Wi-Fi, and move the slider to Off).
In some cases, applying the iPhone 1.0.1 update can ameliorate this issue, though it hasn't been successful for everyone experiencing the problem.
Similar issue? Please let us know.