We walked out with a MB and Gold 7+ Verizon unopened. Put our T-Mobile SIMs in when we got home. Works just fine!
We wanted IUP, but in that case you have to activate in store. We like Interest free to keep our funds in our bank... We went with the 18 Month Interest Free Barclay Apple Visa (this is considered a credit card purchase to Apple). We will have them paid off in time for the 7S or 8 (whatever they call it next year).