As Veltman points out, the AT&T Bell Labs did some of the first digital transmission and switching in 1962, seven years before the "US Internet" began. When the Department of Defense (DoD) commissioned the Advanced Research Project Agency's Network (ARPANET) to do research into networking, it was AT&T that provided 50kbps lines. In 1969, the year that Arpanet began, AT&T's Bell Labs developed Unix which was "the operating system behind the early Internet, and was one of the key operating systems in the middle and late ARPANET."
Between 1969 and 1972, Bell Labs developed the C programming language basic to much of Internet software. In 1970, AT&T installed the first cross-country link between the University of California at Los Angeles (UCLA) and Bolt, Beranek and Newman (BBN) in Boston. In 1976, AT&T's Bell Labs developed (Unix-to-Unix Copy (UUCP), which was distributed with UNIX one year later."
All of these were important points of origin of the Internet as we know it, so the telco theory, unpopular as it is in Internet circles, should perhaps be explored in more detail. Certainly the physical infrastructure created by the telcos was central, and certainly telcos had worked out protocols for sending voice data between disparate networks early in the piece. In the examples above, they added the component of computers and networked them. Can we completely eliminate the telco origins and contributions to early developments?