You still can, and thousands of people do it every day.
The first two telephone numbers a little kid learns are usually 911 and their own.
When I was about 5 years old, I decided to call 911—just to see what would happen, even though I knew I wasn’t supposed to. When a dispatcher answered, I promptly hung up. They promptly called back.
This led to a conversation I suspect many mothers have had with many curious children. It must have been around the same era when I learned of what seemed at the time to be a great secret of telephony. There was another number I could call, and I could call it any time and as many times as I wanted, without getting in trouble.
In Baltimore in the 1980s, if you dialed 844-1212, a pleasant automated voice would tell you the exact time. The message was something like this: “Good morning. At the tone, the time will be 8:55 and 50 seconds.” Then there was a curt beep, and the message would repeat with an updated time. You could keep listening as it counted up in increments of 10 seconds. Eventually, you got disconnected.