Used iPhone 4 vs 4s: Which should you buy?

How to pick the right used iPhone 4 or iPhone 4s for you!

SOLVED: Differences between 4 and 4s batteries - iPhone 4S - iFixit

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How to tell if an iPhone is a 4 or 4S - Quora

How to Tell an iPhone 4 from a 4s: Differences Explained

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Apple iPhone 4S Review > Messaging, App Store, Browser

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Photo of Two Apple iPhone 4 Smartphones

Unlocked iPhone 4 available in the US, but it will cost you