I think the hold function for business phones has been around since the days (which I've only seen in old movies) that there was a live switchboard operator asking you to hold. I don't ever remember thinking of it as anything new, so it must have been common in any business where there were multiple lines when I got my first office job in 1979.
P.S. You didn't ask, but the office also had a fax machine. However, they called it a "telecopier"; I don't remember when facsimile machine got shortened to fax.
