Those in the trade call it a 610 plug
They had a cousin called the 611 plug - used to connect security systems to the vintage copper network - looked exactly the same, fooled many an apprentice
Ah the classic telephone wall plug circa late 1980’s to mid 1990’s, back in the days of dial up modems, dot matrix printers and only five channels on TV which much like today mostly had crap on them.
Thousands were to be converted by 3000 into EV charging outlets by the former Morrison Conservative Cabal🤑. It’s understood a contract had been awarded to a Caymans Group without tender‼️
I’ve still got my landline- still prefer it to mobile- 3 of them in house- easier than trying to get to mobile which is never with me while I do stuff!!
Call me old school but it’s useful!