The iPhone in general is an excellent piece of hardware. However, reports are circulating that after heavy usage of the white iPhone 3G S, the smooth, rounded plastic backing may change from a beautiful pearl white to a burnt light-brown.
IPhone 3G S users are finding that this incident can be caused while using multiple connection sources such as GPS, 3G or Edge at the same time. In this case, this device user was using 3G and GPS. This discoloration and possible battery/ chip set engineering mistake may lead to a mass recall or refund, if more reports of brown-backed iPhones come in. No other solid reports have come in regarding other cases/phones or the black 3G S.
Apple has yet to comment on the situation, as this may only be an isolated incident.
UPDATE - Other reports of overheating 3G S' are coming in. Although not many reports of discoloration, comments on these sites below offer other accounts of such overheating probelms: