T-Mobile has announced they will no longer throttle or cap their unlimited plans. So, if they get the new iPhone next month, there will be a bit of competition for Sprint, and a new option for iPhone users looking to escape the AT&T/Verizon anti-consumer policies.
http://news.cnet.com/8301-1035_3-57497706-94/t-mobile-cuts-the-strings-on-new-data-plan-goes-fully-unlimited/
http://news.cnet.com/8301-1035_3-57497706-94/t-mobile-cuts-the-strings-on-new-data-plan-goes-fully-unlimited/