Doubtful. Samsung was already building a Galaxy S III with AWS support for T-Mobile, as they have with previous Galaxy S devices, and if they weren't, there wouldn't be one for the new entrants. The only thing that has changed is that the Big 3 either can't or don't want to buy exclusivity rights.
Apple has repeatedly passed on making an iPhone with AWS support for T-Mobile's 30 million customers, so the maybe couple of million new entrant subscribers aren't likely to tip the scales there. The only way the new entrants get an iPhone is if T-Mobile gets one with AWS support.