I just changed the battery in my daughters iPhone 3G. Pretty straight forward as I've done it a few times on other iphones (which all went ok!).

The moment I started hers back up though, I got the dreaded "overheat" message with the big yellow triangle.

There's no signs of warmth at all, and it happened the moment it booted up - so I can only say it's false.

Any ideas? I might try just stripping it down again and putting it all back together to see if it's a dirty connector etc. I did blow off everything when it was apart though.