Thanks to this thread TIL it was one of the few serious competitors to ATTs monopoly.

Southern Pacific Communications and introduction of Sprint

Sprint also traces its roots back to the Southern Pacific Railroad (SPR), which was founded in the 1860s as a subsidiary of the Southern Pacific Company (SPC). The company operated thousands of miles of track as well as telegraph wire that ran along those tracks. In the early 1970s, the company began looking for ways to use its existing communications lines for long-distance calling. This division of the business was named the Southern Pacific Communications Company. By the mid 1970s, SPC was beginning to take business away from AT&T, which held a monopoly at the time. A number of lawsuits between SPC and AT&T took place throughout the 1970s; the majority were decided in favor of increased competition.Prior attempts at offering long-distance voice services had not been approved by the U.S. Federal Communications Commission (FCC), although a fax service (called SpeedFAX) was permitted..

In the mid-1970s, SPC held a contest to select a new name for the company. The winning entry was "SPRINT", an acronym for "Southern Pacific Railroad Internal Networking Telephony".