All 600-Series Area Codes

Of all the area code groups, the 600-series is the most overlay-heavy — many of the codes here were added not to cover new geography, but to extend existing metros that had outgrown their original assignments. Boston (617 alongside its overlays elsewhere), Nashville (615 paired with 629), Tampa (645 and 656), Trenton (609 and 640), and the Bay Area cluster of 628 in San Francisco, 650 on the Peninsula, and 669 in San Jose all show the pattern. The range also reaches further into US territory than most: 670 serves the Northern Mariana Islands and 671 covers Guam, both non-state Pacific territories that share the North American Numbering Plan with the fifty states. Mainland coverage is broad — 602 in Phoenix, 614 in Columbus, 617 in Boston, 619 in San Diego, 678 in Atlanta, and 681 in Charleston, West Virginia each anchor distinct regions.

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