Sustainable advantage is quite difficult in any competitive market. So it is in the U.S. mobile market. Some might debate who moved first to lower tariffs across Canada, the United States and Mexico.
A reasonable person might say it was AT&T, promising to make calling between the United States and Mexico as seamless as calling within the United States or Mexico, that prompted T-Mobile US to launch its own offer.
Within short order, Sprint and Verizon Wireless all responded with offers offers of their own.