I have had an iPhone 3, 3GS and 4 and they have all held up extremely well. I have the Otterbox iPhone case for when I deploy for wildland fires etc (mostly to protect it from excessive dust and water). For day to day I carried them in a simpler and more streamlined case and have yet to damage one of them.
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"Trust in God --and press-check. You cannot ignore danger and call it faith." -Duke