Agreed heat is caused by the processor, but if you read the comments, there are other iPhone 3GS owners who did experience "hot potato" syndrome while using bluetooth on the phone. One owner did noticed "browning" of his white iPhone 3GS.

I believe your mileage may vary and if you iPhone runs hot...stop what you are doing and let it cool off. Go to the home screen or shut it off.

You may not want to put a case on your iPhone to prevent it from cooling off.

iPhone 3GS has a much faster processor than last year's iPhone 3G.

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