Dial in using #1

For several years I have been dialing in to zoom with 1 plus area code and number. Recently, my attempts to connect did not work. I got no dial tone when I used the number 1 prior to the area code. So I tried without dialing the number 1 and it worked.  Why has this changed? Should the number 1 be removed from the dial in instructions for audio connection to our zoom meetings?