The founder of MCI (the M stood for Microwave) realized that by using Microwave Relay Towers, he could earn enough profit to pay for a set of towers between Chicago and St. Louis WITHIN EIGHT HOURS assuming a start time of 7:00 am.
That realization, and his outmaneuvering of the FCC, was the beginning of the end for ATT. Ironically today MCI is owned by Verizon.
If you’re interested in learning more check out this book:
The Network: The Battle for the Airwaves and the Birth of the Communications Age https://www.amazon.com/dp/006224275X/