Before I get started, this post applies to the United States.
The Buffalo area was the last major metropolitan area in the United States to have seven digit local phone numbers. Six-digit numbers endured into 1964, I believe, long after the NAP was adopted and nationwide long-distance direct dialing was implemented. My parents bought their first house in 1962, and the label on the New York bell-provided phone read:
AREA CODE 716
(4567 is just an example, but you get the idea.)
Anyhow, if I was in … oh, California, and I wanted to dial this number, could I dial 716-83-4567 or another Buffalo-area six-digit telephone number directly?