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So you have had 3 iPhone 4 that had all the proximity sensor problem? That sounds highly unlikely imho, what is the first thing you do to your new phones?Maybe it's something related to that, are you putting on any type of screen protector or case that might cause the problem?
 
Apple won't. They'll keep swapping with other iPhone 4 models. Even if there was a recall for the iPhone 4, 5 years from now, they'll swap them with the iPhone 4. Just like they did for the iPod Nano 1st Gen recall recently.
 
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