I've been buying and selling used iPhone, and have gone through all generations, each used a year or more.
(Purchase Price / Sold Price)
iPhone 8GB (250/220) -> iPhone 3G 8GB (200/200) -> iPhone 3GS 16GB (270/220) -> iPhone 4 32GB (250/300) -> iPhone 4S 32GB (400/Now)
iPhone price drops quite fast within 6 months of release, but the used iPhone price stay quite steadily.
And with a good opportunity, you might not spend much upgrading to the latest gadget.
(Purchase Price / Sold Price)
iPhone 8GB (250/220) -> iPhone 3G 8GB (200/200) -> iPhone 3GS 16GB (270/220) -> iPhone 4 32GB (250/300) -> iPhone 4S 32GB (400/Now)
iPhone price drops quite fast within 6 months of release, but the used iPhone price stay quite steadily.
And with a good opportunity, you might not spend much upgrading to the latest gadget.
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