Almost there. Now all we need to know is what firmware you currently have on your iPhone. Click here to learn how to find out:

iOS 3.1.2
iOS 3.1.3
iOS 4.0
iOS 4.0.1
iOS 4.0.2
iOS 4.1
iOS 4.2.1
iOS 4.3
iOS 4.3.1
iOS 4.3.2
iOS 4.3.3
iOS 4.3.4
iOS 4.3.5
iOS 5.0
iOS 5.0.1
iOS 5.1
iOS 5.1.1