Originally Posted by Commodore 64
(The yellow triangle voids the warranty, and triangleaway might not work on S5)
Unless you really piss someone off at AT&T, then they (in the past anyway) usually don't care if you rooted your phone. As long as it's a verified "mechanical" issue and not a software problem, then I've never heard of anyone being denied warranty claims.
Take that with a grain of salt though. It's certainly not "set in stone" and is subject to change with the wind.
There was one developer awhile back who was a bit of an ass. He hard bricked his phone and tried to get it warrantied and he was denied when Samsung said it was his software that caused a CPU issue. I think they "knew" him though.