Question: When did phone numbers change to 7 digits?
Answer: from the 1950s onward
Disambiguated annotations:
qaPairs: question: When did North American plan to change all phone numbers to 7 digits get accepted?
answer: October 1947
question: When was the first new area code received by a locale, an indication of when North American phone numbers changed to 7 digits?
answer: 1947
question: When was the first customer call using the NANP made, an indication of when North American phone numbers changed to 7 digits?
answer: November 10, 1951