You are all missing the point. Think about it, Sprint, most likely, will offer special incentives to AT&T and Verizon customers to switch. If they are willing to pay 20 Million for the iPhone, they could offer customers from AT&T and Verizon a price they can't refuse. They would get them for the 2 year contract, and if they leave early, then those that would want to leave, would have to pay $350. Sprint gets there money back either way, but gains a lot of new customers.
With Apple, never say never. Money talks, and you know the rest.
Apple didn't say Verizon and AT&T wouldn't get the new iPhone 5, but instead of getting, launch time, which looks like it would be in October, they would get in the beginning of 2012, most likely by the end of January. Which is only 3 months. So basically Sprint would pay 20 million for a 3 month window, not 3 years. Sounds like a deal for Apple and Sprint for such a short time.
Now the question, will Sprint let my wife upgrade a little early to get the new iPhone. She hates her Epic 4G and wants an iPhone, but won't pay full price for it.