Depends on how much storage you need for your iPhone. The biggest one is 16GB which may or may not be enough for storage, music wise. I love the applications you can get on it, it looks fantastic and the games play well on it too. The camera on the other hand is very disappointing, there's no flash and only 2mega pixel. And hte battery life is horrendous too. But have a look anyway...
http://www.apple.com/iphone/specs.html
Here's some specs to help you make up your mind.
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