iPhone 3GS (click for larger image)

While not acknowledging a problem, Apple has added the iPhone 3GS to the heat-management advice it has given for the older version of the smartphone.

The support page originally explained how to keep the iPhone 3G within "acceptable operating temperatures." As of June 25, the company included the iPhone 3GS under the same advice.

Users of the iPhone 3GS, which Apple started selling June 19, have been complaining that the gadget runs too hot. In the case of the white model, the heat has been sufficient to cause discoloration.

Users have said through various blogs and forums that the overheating tends to occur while using applications that tap the iPhone's GPS and 3G wireless components. Apple has not acknowledged a heat-related problem with its popular smartphone, but the company has posted some advice on preventing iPhones from running too hot.

First, the device should only be operated when the external temperature is between 32 degrees and 95 degrees. "Low- or high-temperature conditions might temporarily shorten battery life or cause the device to temporarily stop working properly," Apple said.

Also, the iPhone shouldn't be stored in a place where temperatures are lower than 4 degrees below zero or higher than 113 degrees. This means the gadget shouldn't be left in a parked car in the sun.

If the iPhone's interior temperature exceeds the device's limits, then it could stop charging, its display my dim, or the cellular signal may weaken. A warning may also appear, telling the user, "iPhone needs to cool down before you can use it."

The message is meant as a safety mechanism to protect components within the iPhone, Apple said. Besides leaving the iPhone in a car on a hot day, other activities that may cause the device to overheat include leaving it in direct sunlight for extended amounts of time and using GPS tracking and certain other applications in hot conditions or direct sunlight for long periods of time.

Despite the heat-related advice, the iPhone meets safety standards set by the International Electrotechnical Commission, according to Apple.

Last summer an Apple 3G iPhone user said he fell asleep with his 3G iPhone in his pocket and awoke with a burn on his leg.

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