from Hacker News

Sign a 2-year AT&T contract, get a free iPhone 4 8GB (Black), sell it on eBay for around $350 (my auction is already at $355 with 2.5 days left), then order that sexy slab of glass and unadulterated Android magic on the 13th.

Three tips! 1. Check the prices on eBay of all the free/low cost phones your carrier is offering. At the moment the iPhone 4 8GB (Black) edged out others, but that could change. Particularly if a lot of people do what I did, although the market seems to have a normal supply at the moment. 2. Don't open the sealed phone box, it's will sell for more if it's "unopened, factory sealed". 3. I don't have a ton of evidence to back this up, but I included photos of taking the phone box out of the AT&T shipping box along with all the AT&T papers, which I believ gives bidders greater confidence and will raise the auction price.

I know this is fairly obvious to a lot of people, but I thought it might be helpful for people that only consider getting free phones on contract.