Yup, was the same in the US, you could only plug in official Bell System products - no third party phones, answering machines, or other unapproved equipment. With the breakup of ATT and the Bell System, it became legal to get your own equipment and plug it in on the phone network. Back in those days, you didn't own anything (at least residential customers), the phone was rented with a monthly charge on every bill. Though if it happened to break, they would just put a new one in, no problems. Those old phone seldom broke though, they were built like tanks.