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The OP explains in a later comment that, he used a floppy-disk based licensing system in the early days of this software.

I worked on a team in 1993 that made point of sale software that "phoned home" and required customers to purchase a modem with the software. We were no cutting edge software company, so I can easily imagine others doing this a few years earlier.

Maybe it literally phoned home... over a 300 baud modem.

I suppose it could have literally "called home" by using a modem to dial a phone number and connect to a dial-up modem on the authorization server. Since it only does this "every few months", that wouldn't be a prohibitively expensive form of communication.