RC1024, good information for E_Ack! Sprint Magic Box is an all-wireless LTE small cell that connects wirelessly to a nearby Sprint cell site while the AIRAVE covers a much smaller indoor only footprint and it boosts voice and 3G data service only. You can click here for more details.
Yep, if you decide to leave Sprint (NOOOOOOOoooooooOOOo!), you'll need to a return kit to send back that Magic Box, just as you would an Airave. If you were to keep it, you'd 1) have a brick, it only uses band 41 and that's ours exclusively and 2) be charged a non-return fee. As part of the cancellation process, you're typically mailed out a return kit.
But you know you want to stay
Wanted to mention here that thousands of Sprint customers have signed up for a Magic Box since we announced it. It was mentioned at launch that availability should start picking up 6 - 8 weeks from now so don't be concerned if you filled out the form last week and have not yet heard back.