The moves by Sprint and AT&T come after No. 4 U.S. operator T-Mobile was able to report three full quarters of customer growth after four years of losses.
AT&T did not change its service rates, but it is offering customers a $200 credit to switch to its network. The company is the easiest target for T-Mobile, which it tried to buy in 2011, since they use the same technology, so it is simple for customers to switch between services.
Their battle got more personal at the Consumer Electronics Show in Las Vegas when AT&T kicked Legere out of its party, a concert featuring rapper Macklemore.
Previously, at T-Mobile's own event, Legere took to the stage to make fun of AT&T and its executives.
Competition could escalate further later on this year when Sprint, which is 80 percent-owned by Japan's SoftBank Corp, is expected to try hard to take back customers who have left because of technical problems from a network overhaul.