Apple is expected to -- what most have named "iPhone 5," although that may not be what Apple calls it -- during a media event at its Cupertino, Calif. headquarters Tuesday at 10 a.m. PT.

Interest in the new iPhone is high, said Jeff Trachsel, the chief marketing officer at NextWorth, judging by the volume of trade-in transactions the company has conducted in the last week.

That was when NextWorth kicked off a promotion that for any 16GB or 32GB iPhone 4 that runs on AT&T's network. The deal expires today.

"Volume is running about 15X-16X above prior to the announcement [of the promotion]," said Trachsel. "We've seen a huge spike, and we're on track to have our biggest [iPhone trade-in] day ever."

"The number of iPhone trade-ins has doubled over the past week," echoed Anthony Scarsella, the chief gadget officer at rival Gazelle. "Last year we did a total of 30,000 trades around the iPhone 4, and it looks like this year that will double."