Some owners of the Apple iPhone 3GS model have had trouble with the model overheating and becoming discoloured.

Details of the problems, which also plagued the older model, have been posted on forums and technology sites. One user claimed he bought an iPhone and used it normally. However it became hot and he said there is a red burn mark on the back.

Another post on the MacRumour forum said: “These are the same problems Apple has had on a lot of other products. You would think they would have gotten it by now. You would think that after the third iPhone they would have gotten it.”

In a statement on its site Apple advised iPhone users to ensure the phone was not left in a car where temperatures could exceed the -20C to 45C range in which the iPhone 3G and iPhone 3GS models were designed to function.

“If the interior temperature of the device exceeds normal operating temperatures, you may experience the following as it attempts to regulate its temperature.

"The device stops charging, display dims, weak cellular signal, temperature warning screen appears with the message iPhone needs to cool down before you can use it,” it said.

However, it seems that there are also other problems affecting the phone. In a posting on the macrumors.com forum, one user complained that using the new device's video recording feature had caused it to overheat, while another complained that after carrying his phone in a backpack, it got so hot that the plastic case became distorted with tiny bumps.