Before CALEA, surveillance was not "built in" to the phone system. Back when Guliani was a prosecutor, taking down the New York mafia, he wrote in his book that the FBI had to pay New York Telephone for a wired connection into any phone they wanted to tap. It really was a wired connection, manually wired onto the main distributing frame, and billed as a private line to a third location. On one occasion the FBI didn't pay their bill, and New York Telephone billed the party being wiretapped. That was part of the motivation behind CALEA.

Electromechanical end exchanges did not log call data for local calls. Some of them counted it, with racks of little counters, read once a month. Toll switches had a logging system involving a wide paper tape. No cheap storage devices existed in the electromechanical era.

What's now referred to as a "pen register" is today an extract from switch logs. But at one time, it was a real physical device. A device that put dashes on a paper tape to log dial pulses. I own one, and it's the one shown in Wikipedia.[1] Mine is hooked up to a dial and some circuitry for demos. You wind it up with a big brass key. The first dial pulse starts the clockwork moving, and it continues to run until there have been no dial pulses for a few seconds. Someone had to hook one of these up to a specific line to track what was being dialed.

That's what the Supreme Court was talking about when, in Smith vs. Maryland, Justice Blackmun wrote "Given a pen register's limited capabilities, therefore, petitioner's argument that its installation and use constituted a "search" necessarily rests upon a claim that he had a "legitimate expectation of privacy" regarding the numbers he dialed on his phone."

The "limited capabilities" are a lot less limited today than they were in the wind-up era.

[1] https://en.wikipedia.org/wiki/Pen_register