All four of the aforementioned wireless carriers are tier-1 carriers, meaning they don’t borrow network capacity from anyone else. These four tier-1 operators have been busy acquiring tier-2 and tier-3 carriers in an attempt to broaden its subscriber base, leaving very few independent tier-2 and 3 operators in the US. An example of a tier-2 carrier in the US is U.S Cellular, who has an agreement in place with Sprint for voice and data coverage.