How to read a US phone number (NPA-NXX-XXXX)
Three parts
+1 646-212-0345 decomposes into: country code 1 (the whole North American Numbering Plan), area code 646 (Manhattan), prefix 212 (a specific central-office code anchored to the New York City rate center), and line number 0345 within that prefix's 10,000-number block.
Format rules
Both the area code and prefix follow the NXX pattern: the first digit is 2–9, the next two 0–9. That is why no US code or prefix starts with 0 or 1. Codes with identical last two digits (800, 888, 877...) are reserved as Easily Recognizable Codes for services like toll-free. N11 combinations (411, 911) are service codes, excluded from assignment.
What digits reveal — and don't
Area code and prefix identify where the number was issued and which carrier held the block. They say nothing about the individual subscriber: that mapping is private carrier data, not part of the public numbering plan.
Sources
FAQ
Why do movie numbers use 555?
The 555 prefix is largely reserved; 555-0100 through 555-0199 are set aside for fictional use, which is why Hollywood numbers cluster there.