The Gaming Table says Pop's opened in 1972. This cover appears to be earlier, and Anderson's ashtray books puts the opening at 1964. Possibly, there were only slots till 1972??

Anyway, I like the phone numbers! There is a later cover from Pop's with almost the same design but the phone now has a seven-digit number (no area code, though). Notice S&H Green Stamps instead of a players club [g].