Why does gazelle.com want your iPhone?

What do they do with the older ones?

I think they refurbish them and resell them

They want them so they can Sell them, even broken ones they Fix em' up and Sell them for a good profit.

They are a reseller. Basically they do the legwork for you. Good company, but you can get more from other sites. I used TechPayout.com and was extremely happy. I think at the time they paid about $20 more for my iPhone.