The issues surrounding Apple's overheating iPhone 3G/3GS have been well documented and have coerced the company to update its support page and include suggestions on how to keep your phone working fine.
We've managed to compile a list of ways on how you can keep your iPhone cool although many of you might disagree.
(1) Move to cooler countries
Apparently, Apple wants you to use your iPhone in a temperature range between 0º and 35º C. The only way to make sure temperature remains constantly between those two limits is to move to a cooler country where the sun is not as harsh. Iceland is a great choice because of the current economic conditions which makes life there cheaper.
(2) Fit it with a cooling appendage
The other way of cooling your iPhone is to use a cooling accessory. Now, back in 2001, boffins at Purdue University came up with a piezo electric fan so small its blades are roughly the width of a human hair.
The other way of doing it would be to get this Physicool First Aid Kit Cooling Reusable Sports Bandage which is marketed as a "Cool gift for sportsmen". Except you will use it on your iPhone. It works by combining cooling with compression and works by drawing heat out by rapid evaporation.
(3) Minimise your iPhone usage, get a second phone
Why not use another phone instead of your iPhone for casual talking? It's the equivalent of using your bike for short distance journeys instead of your Jaguar car.
You can either go for a really cheap model like the Alcatel OT 227 which costs £4.95 when purchased with £10 airtime. Admittedly it defeats the purpose of having your iPhone in the first place but then, at least you will be able to phone AND watch movies at the same time.
(4) Pester Belkin To Come up with an accessory
... Or yo could start a petition. You can expect companies to start shipping cooling accessories for the iPhone. The Belkin iPhone 3 silicone sleeve could be modified to integrate a cooling feature. Sleeves are popular but are not exactly ideal to dissipate heat, which could make worst especially in hot weather. Maybe someone will bring the equivalent of a laptop cooler but for the iPhone.
(5) Mod Your iPhone
Modding your phone will cost you money and will invalidate your phone's warranty, almost certainly. So it is better to go ahead at your own risks.
GeekTechnique has an old project where it shows how to modify your iPhone's appearance. We have yet to find how you can actually do it though. Furthermore, there has been discussions going on about having an underclocking app for the iPhone and the iPod touch.