Overheating
Shortly after the release of the iPhone 3GS, some users reported overheating of the device while in heavy use, and others reported discoloration of the device due to heat (particularly on the white models). The discoloration issues were largely discounted as being as a result of iPhone covers rubbing against the back of the iPhone.[17] Apple responded to the heat issue reports by warning users against leaving their iPhones in a car on a hot day, leaving it in direct sunlight for extended periods of time, and refraining from heavy usage while in a hot/sunny environment.[18] It is also worth pointing out the temperature specifications in which the iPhone should be operated, which follows safety standards in the countries the 3GS was released.[