For those of you who may still be wondering, or may be thinking of switching from an Non-Apple smartphone to the iPhone, iOS 7 works on the following iOS devices:
iPhone 4
iPhone 4S
iPhone 5
iPhone 5C
iPhone 5S
iPad 2
The New iPad (iPad 3rd Generation)
iPad (4th Generation)
iPad Mini
iPad Mini with Retina display
iPad Air
iPod Touch (5th Generation)
iPhone 4
iPhone 4S
iPhone 5
iPhone 5C
iPhone 5S
iPad 2
The New iPad (iPad 3rd Generation)
iPad (4th Generation)
iPad Mini
iPad Mini with Retina display
iPad Air
iPod Touch (5th Generation)