Apple updates online support for keeping iPhone “within acceptable operating temperatures”
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In a move that may or may not be in response to recent reports of iPhone 3GS overheating (and discoloration in the white models), a knowledge base article for iPhone 3G and 3GS was updated on June 25, 2009 and provides a screenshot of the iPhone screen that reads, "iPhone needs to cool down before you can use it". Apple recommends operating temperatures of 32º to 95º F.