Thanks Julien. :)
I think our salesperson was just a bit too anxious to make the transaction, which explains why she came back w/ an additional requirement (phone bill) the following day.
But as far as I'm concerned, once they take our money and sign the deal, there is no going back - if the bank needs anything that wasn't mentioned to us in the first place, the dealer will have to take it on himself. You don't add requirements once the deal is done, period. Though we did try our best to provide a few additional papers, because, well, we're nice people. ;)
Anyway, we finally found yesterday - after we went back to the dealership to provide a few extra papers - that Sprint accepted to sign contracts when you provide a deposit upfront, and since I needed a phone too, we went w/ that option. And we found out that we also had a discount w/ them, so... The good thing is that all those things will help w/ credit in the future, so we might as well put up w/ it now. So we would be able to provide the paper if the bank insisted.
We've been here for 11 days and it feels like 3 or 4 weeks, so much time we've spent at the DMV, the car dealership and all that fun stuff. But the Jeep is ours, and we finally can enjoy the vacation.
But that's a lot of $, so the audio interface will indeed have to wait. Still, thanks for the link Grant. I hadn't heard about that one - I'll check it out.