I don't even remember the last time I went into a brick and mortar store to buy a cellphone. Years ago (before the iPhone), I would go into the store to look at all the brands and models, and buy one there. But the last 5 years or so, when I need a new phone, I just log into my account, select the phone I want, and have it shipped to my house in 1-2 days.
At this point the only real "decision" for most people is iPhone or Samsung Galaxy, then what color, and how many GB, that's it. Why go into a store for that. I don't see how this "store within a store" is going to work, why would Sprint need thousands of these stores. Sprint is going to go out of business if they lease the thousands of RadioShack stores that also couldn't turn a profit selling cellphones. What would Sprint be able to do different in these stores?