"Skating to where the puck is going to be" is an old Wayne Gretzky saying that Steve Jobs once quoted, and so it gets rehashed a lot when discussing Apple's strategy for moving into new markets. Typically that's with hardware like iPhone, iPad, or potential hardware like the rumored iWatch, or with features like iTunes, AirPlay or Passbook. It's also an apt way to describe Apple's commercial strategy.
Sprint sold a total of 1.8 million iPhones during Q4 2011, with 40 percent of those going to new customers. Admittedly, 1.8 million is only about a quarter of the 7.6 million iPhones AT&T sold during the same period, and less than half the 4.2 million moved by Verizon, but considering Sprint's 55 million customers ranks as the the third largest U.S. wireless carrier, and this is the first official quarter that Sprint had the iPhone to sell, it still indicates a fairly solid adoption by their subscribe base.
In a company blog post earlier today, Cole Brodman, Chief Marketing Officer for T-Mobile USA, told customers that they were interested in offering a "no-compromise iPhone experience" on their network, but offered little details on the negotiations between the carrier and Apple.