When the iPhone went on sale through Verizon for the first time earlier this month, it set records for sales rates, and forced Verizon to stop pre-sales after less than 18 hours due to overwhelming demand.

While there is no shortage of first-time iPhone owners who have been champing at the bit for the wildly popular smartphone to break free from notoriously spotty AT&T service, it's a safe bet that plenty of those new sales came from current iPhone owners trying to break free themselves from AT&T.

The question from an environmental perspective is: What will happen to all those iPhones? Although throwing away a functioning iPhone is not likely to be a common occurrence, it's yet another example of the iPad phenomenon of last year: One shiny new gadget replaces a slightly older version, potentially sending thousands of devices into the e-waste bins of history.

In an attempt to make it easier for new iPhone owners to sell their unwanted smartphones in a way that will see them reused, not recycled, eBay last week kicked off a two-week-long promotion in its Instant Sale project: Cash guarantees of $200 to almost $450 for smartphones from Apple, Motorola, Samsung and HTC.

Instant Sale, launched last fall, makes it a simple, four-step process to sell back functioning electronics, with a flat price offered and free shipping for sellers. Now eBay is moving to take advantage of the booming phone resale market.