Before it can be used on the modern plug and socket arrangements a vintage telephone needs to be converted. This involves little more than fitting a new line cord with a plug but it's quite an important "Little more."
There are plenty of web-sites saying how to do this but a lot assume that the 'phone hasn't been messed about with in the past. The following ones have diagrams showing full details how things should be done.
This shows the details of the 332 — the big chunky Bakelite ones from the 1940s and 1950s — and this the 700-series — the plastic ones from the 1960s to 1980s.