There has been a lot of outcry over several issues relating to iPhone 4 in recent weeks like iPhone 4's antenna problem and also the proximity sensor. One issue though has managed to stay relatively under the radar so far.

Some iPhone 4 users have been noticing poor quality voice output when their phone is paired up with a Bluetooth device. 

One of our readers, Greg has written to us about his experience:

"I received my iPhone 4 and paired up my Bluetooth devices. I have two Motorola mono headsets, a Jawbone, a stereo Altec Lansing, and a stereo Motorola Bluetooth. I have tried all the devices and everyone I talk to exclaims they can not understand me. They say the sound is muffled, weak and distorted. If I answer the phone and then connect the Bluetooth device the audio is even worse. I use Bluetooth exclusively and my iPhone 4 is of no use to me. I had to switch back to my 3GS so I can use Bluetooth."

A thread on Apple's discussion board about this issue has been seeing a lot of activity in the past few days. Apparently, folks at Apple Genius bar too have been unable to solve the problem. A forum member from Singapore complains:

I'm having the exact same problem. Ever since iPhone 4 was released in Singapore on 30th July, i've tried in vain to use my Plantronics Discovery 925 with it. This is the same Bluetooth earpiece I used with my previous phone, which was the iPhone 2G

Problems include..

1. Very muffled

2. Distorted signal

3. Dropped calls. 

None of this happens when i'm off my earpiece, and it is very frustrating while driving. 

Another forum member writes:

"Yesterday, myself & a Genius Bar Tech tested several BT headset brands & two iPhone 4s. We both witnessed that turning the BT headset from OFF to ON durning a call and then switching from phone to BT will cause poor sound quality 100% of the time. He simply said this will have to be something fixed in an a future update."

It is not clear whether the issue is with the hardware or with the iOS. While Greg tells us that he does not face the issue on his iPhone 3GS running iOS 4, some users seem to have started noticing this issue on their iPhone 3GS only after upgrading to the new version of the operating system. Also, while the latest iOS 4.0.2 update does not seem to have fixed this issue, Apple Support staff appear to have however acknowledged the problem and have indicated to a few customers that an update is on the way.

Are you facing similar issues with Bluetooth on your iPhone 4? Tell us your experience in the comments below.

Thanks Greg for the heads up!

Update:

iOS 4.1 will fix proximity sensor and Bluetooth problems

[via Apple Support]