I've noticed that my bluetooth connections are much better and connect much faster on the iPhone 4...I have an older (maybe 4 years old) set of bluetooth headphones that I had a terrible problem with connecting to my 3GS on 3.x.x. The same headphones connected immediately to my iPhone 4 with excellent audio quality...I'm not sure if it is the phone itself or the iOS4 (or perhaps a combination of both), but it is a NOTICEABLE difference...
Also, people have been telling me that my voice quality from the bluetooth connection in my car is better as well...
Also, people have been telling me that my voice quality from the bluetooth connection in my car is better as well...