Sprint has some sort of group-buying promotion called
Sprint Ticket Takedown (expired) where the more people register their e-mail and cell number, the lower the price of a movie ticket you can get from either Fandango or MovieTickets.com. You can register any time before 8/14, but you must come back on 8/15 to buy the tickets. One day only.
According to the fine print, only 100,000 tickets will be available, and each registrant can buy two. As of 8/9, there are already over 87,000 registrants. If that number reaches 95,001 then the ticket price will reach the lowest possible $4. I think that’s a pretty safe bet, so you’ll probably want to come back pretty early on 8/15 (opens 12:01am Eastern, so even late Sunday night for some). (Update: It worked, I got two tickets for $4 each at Fandango.com. Sweet!)