To close those deals, consumers must agree to a new two-year contract with a mobile carrier.

Also as expected, the number of people considering selling an older smartphone soared yesterday as Apple confirmed that the iPhone 5 has a larger 4-in. display, supports mobile carriers' faster LTE data networks, and is both lighter and slimmer than its predecessor.

Gazelle tracked a 75% increase in the number of quotes it offered yesterday compared to Tuesday. CExchange, an electronics trade-in firm that handles programs from 40 brick-and-mortar retailers, mobile carriers and online sources, including eBay's Instant Sale, Wal-Mart and Radio Shack, cited a 70% jump in appraisals yesterday.

According to Scarsella, this year's volume shows a much greater interest in the iPhone 5 than took place last year when Apple introduced the iPhone 4S. "Compared to last year, we generated half a million offers. That's 1,200% over the same day last year," Scarsella said. At one point on Wednesday, Gazelle was buying about 30 used iPhones per minute -- a pace of 1,800 per hour.

"It was crazy," said Scarsella.