They work great on the iPhone/iPod. I have the exact same iPhone as you, and I love them. Controls are great. III's controls are especially spiffy because a virtual joystick shows up wherever you put your finger.
It doesn't matter what order you play them in...unless the game has a direct sequel (X-2, XIII-2, etc.), the story isn't continued in the next game. However if you are choosing between 1 2 and 3 on the iPhone, I'd suggest playing 1 first...just because its shorter than the other two, and it has the weakest story (nameless characters). If you play the other two first it might be harder to enjoy the first game. Its still a lot of fun though!
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