Where in North America is area code 504?

Area code +1 503 is the area around Portland, Oregon, including Salem and Astoria, as well as Aurora, Bay City, Beaverton, Falls City, Lyons, Mill City, Newberg, and Sheridan. Area code +1 971 is an overlay on the entire 503 area.

Originally, area code 971 was an overlay only on the inland part of 503, including Portland and Salem, but not including the coastal areas from Astoria to Tillamook and Lincoln City. However, the overlay was expanded to cover the entire 503 area.

International country code +503 is El Salvador.

(The plus sign means "insert your international access prefix here." From a GSM mobile phone, you can enter the number in full international format, starting with the plus sign. The most common prefix is 00, but North America (USA, Canada, etc.) uses 011, Japan uses 010, Australia uses 0011, and many other countries use different prefixes.)