Yesterday: bought a new iPhone 4 (16gig) for $200
Today: sold a 2 year old iPhone 3G (8gig) for $175

There’s an upside to AT&T lock-in: the resale value of the older iPhones stays nearly as high as what was paid years ago, and so it costs almost nothing to upgrade every 2 years.

In my case, I’ve actually saved money by getting a brand new phone. Since AT&T now has tiered data plans, my new contract is now cheaper each month than it was previously, offsetting the $25 hit I took on the hardware.