Sprint is the only current major U.S. wireless carrier to still offer true unlimited and unthrottled wireless data and if they can keep this offer in place with an iPhone 5 in hand then they may see people leaving AT&T and Verizon to get an iPhone without worrying about data and also getting some of the best prices around. Sprint also lets you call mobile phones without limit, even on their lower cost 450 minute anytime plan. And finally, they offer unlimited text messaging with most of their calling plans. The bottom line is that Sprint has the best data, voice, and messaging plans and if they then offer one of the best mobile phones available they could be the preferred iPhone carrier.
I doubt we will see LTE or WiMAX 4G in any of these new Apple iPhone devices, but think people won't mind that if they get lower cost unlimited data and messaging with an iPhone 5 and iOS 5 experience. I think it is great news if more carriers get the iPhone as that will help populate the iOS platform for iMessage and other Apple services.
If Sprint gets the Apple iPhone 5 they may also not be so fired up about the AT&T and T-Mobile deal. AT&T has the iPhone now and will get the next version, but many people are not happy with the service they get from AT&T (including me) so having multiple CDMA choices is a good thing.