Telephone

Alexander Graham Bell receives a US patent for the telephone in 1876 and demonstrates a call that year. Elisha Gray files a caveat the same day. Antonio Meucci and Johann Philipp Reis had earlier voice devices. Bell's patent and company are what turn it into a network.

The contribution is a voice, not a code. You do not need an operator who knows Morse. Businesses and families adopt it because the interface is speech. The network of switches and wires built for phones is later reused, in part, for data.

A telephone is a microphone, a speaker, and a current, all of which descend from Faraday's experiments and the telegraph's wires. It does not add a new physics. It adds a use that people will pay to have in every town.

The 1876 date is the patent and the famous demonstration, not the day the last town was connected.