More common (at least as reported in a variety of reader forums) are reports of iPhones running hot--but not hot enough to do any damage. The main complaint is that the iPhone becomes sufficiently warm so that actions, such as putting the phone to your cheek to make a phone call, become untenable. and have both described personal experiences with a too-hot iPhone 3GS.

If your new iPhone 3GS has ever had this symptom, you might want to take a deep breath before assuming that either you need a replacement iPhone or that Apple needs to issue a recall.

First of all, this symptom is not new to the iPhone 3GS. It has been an occasional issue with all previous iPhone models. For example, describes a heat problem with iPhone 3G models running iPhone OS 2.2.1. According to this report, the heat could reach a point where Wi-Fi connections were lost. Still, many users have never had any such symptom. Even those phones that have heated up appear to run well after cooling down and likely do not require any hardware fix.

, if the internal temperature of your iPhone gets to a point where the "operating temperature has become too hot," a message stating the "iPhone needs to cool down" should appear on your screen. If you have never seen this message, your iPhone is likely fine--even if it sometimes feels warm to the touch. If you have seen this message, your iPhone is probably still okay. Yes, I assume it's possible that the iPhone could overheat to dangerous levels without generating this message, but this is not common.

Still, there does appear to be a non-trivial issue here. As again , and as I can personally attest, Apple Geniuses can use diagnostic software on a Mac to check for serious iPhone overheating. Apparently, if the program shows that an internal heat sensor has been tripped, you may qualify for a new phone.