A Chinese forum member from here claims that the iPhone 3GS is capable of playing both 720p and 1080p video, encoded with H.264. The only problem is that Apple artificially limited playback resolution to 640 x 480 pixels. Do we really need such playback quality on the go and are you up to sacrifice the handset’s battery life for better resolution?
Turns out that a member of the above-mentioned forum managed to go past Apple’s restriction and played a 1080p video at 30Mbs on his iPhone 3GS. Even a Macbook would have a hard time pulling out this stunt so imagine the overheating and battery depletion of the poor handset.
Basically, you CAN play Full HD videos on your iPhone 3GS, but do you really want to? I’m guessing that after one hour of HD playback your battery will go from 100% to zero or even faster than that, so you can’t even watch a full movie.