Area codes 503 and 971 (English Wikipedia)

Analysis of information sources in references of the Wikipedia article "Area codes 503 and 971" in English language version.

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archive.org

Mabbs, Ralph (Winter 1947–1948). "Nation-Wide Operator Toll Dialing—the Coming Way". Bell Telephone Magazine. 26 (4): 181. Retrieved 2023-08-10.

"Split of 503 (Oregon) Numbering Plan Area (NPA)" (PDF). North American Numbering Plan Administration. May 19, 1995. Retrieved May 25, 2012.
"Concentrated Overlay of 503 Numbering Plan Area (NPA) with 971 NPA" (PDF). North American Numbering Plan Administration. July 21, 1999. Retrieved May 25, 2012.
"Permissive Dialing Extended for the 503/971 Concentrated Overlay (Oregon)" (PDF). North American Numbering Plan Administration. December 10, 1999. Retrieved May 25, 2012.
"Expansion of the Concentrated NPA 971 Overlay with NPA 503 (Oregon)" (PDF). North American Numbering Plan Administration. December 21, 2006. Archived from the original (PDF) on November 26, 2010. Retrieved May 25, 2012.

"Expansion of the Concentrated NPA 971 Overlay with NPA 503 (Oregon)" (PDF). North American Numbering Plan Administration. December 21, 2006. Archived from the original (PDF) on November 26, 2010. Retrieved May 25, 2012.