In the 1930s, Claude Shannon was trying to optimize the phone network's automatic switching fabric built out of millions and millions of relays when he, more or less by accident, proved that switching circuits are equivalent to Boolean algebra, in a deep sense, and so the appropriate arrangement of switches, can compute anything that can be computed.
The first major commercial application for the vacuum tube was not in radio, but in amplifying long-distance telephone links. They would quickly find use in frequency multiplexing telephone lines, too. [1]
Similarly, one of the first applications of vacuum tubes as a high-speed electronic switch was for multiplexing telegraph lines, and much of the initial research on high-reliability low-power tubes able to switched fully on without damage began, with the telephone and telegraph companies.
The first computers were built out of relays and vacuum tubes specially designed for telecommunications.
The transistor was invented at Bell Labs. The planned application was the telephone network. The very same year, the theory behind modern error correcting codes was developed at Bell Labs too. These find extensive use today in data storage in computers, but the original goal was arbitrarily accurate transfer of telegraph data over noisy links.
Digital transmission of photographs dates to the late 1920s too; they wanted to send images over extremely noisy long-distance telegraph links. So record the intensity of light over each spot of the image on paper tape. Then send the tape over the wire. And reverse on the other end. [2]
I've come to understand the computer revolution as really the story of the telecommunication revolution. Computers serendipitously came about with advances in telecommunications, enabled by the same technologies, and indeed, often driven by the needs of telecommunications. (One of the very first applications for a computer in an embedded context - dating to the late 1950s in experiment - the telephone exchange, of course.)
[1] https://long-lines.net/tech-equip/misc/Graybar103-0693.jpg