| 301 | Maryland (Hagerstown, Frederick, Rockville, Cumberland and western Maryland, overlays with 240) |
| 302 | Delaware (all) |
| 303 | Colorado (Boulder, Longmont, Aurora, Denver and central Colorado, overlays with 720) |
| 304 | West Virginia (to be overlayed by 681) |
| 305 | Florida (all of Miami-Dade County and the Florida Keys of Monroe County: Miami, Homestead, Coral Gables, Key West; overlaid by 786 for all of Miami-Dade but not Keys) |
| 306 | Saskatchewan (all) |
| 307 | Wyoming (all) |
| 308 | Nebraska (North Platte, Scottsbluff, McCook, Kearney, Grand Island and western Nebraska) |
| 309 | Illinois (Peoria, Moline, Rock Island, Galesburg and central western Illinois) |
| 310 | California (Malibu, Torrance, South Bay, Beverly Hills, Santa Monica, Catalina Island, the Los Angeles Westside, and the coastal suburbs of Los Angeles County, overlays with 424) |
| 311 | Local or government non-emergency use, City Hall in some localities. |
| 312 | Illinois (downtown central Chicago area) |
| 313 | Michigan (Dearborn, Detroit and inner Detroit suburbs) |
| 314 | Missouri (St. Louis, Florissant, Crestwood, Affton, and surrounding Missouri suburbs) |
| 315 | New York (Syracuse, Utica, Watertown, and north central New York) |
| 316 | Kansas (Wichita, Augusta, El Dorado, Mulvane and the Wichita surrounding area) |
| 317 | Indiana (Indianapolis, Carmel, Greenwood, Mooresville, Beech Grove and central Indiana) |
| 318 | Louisiana (Shreveport, Monroe, Alexandria, Fisher, Tallulah and northern Louisiana) |
| 319 | Iowa (Burlington, Iowa City, Cedar Rapids, Waterloo and east central and southeastern Iowa) |
| 320 | Minnesota (St. Cloud, Alexandria, Morris, Hutchinson, Sandstone, Appleton and central Minnesota) |
| 321 | Florida (Orlando, Cocoa Beach, St Cloud and central eastern Florida, partial overlay with 407) |
| 323 | California (Florence and Los Angeles excluding downtown Los Angeles; see also 213) |
| 325 | Texas (Abilene, Sweetwater, Snyder, San Angelo) |
| 330 | Ohio (Youngstown, Warren, Akron, Canton and northeastern Ohio, overlays with 234) |
| 331 | Illinois (West Suburban Chicago, overlays 630) |
| 334 | Alabama (Montgomery, Auburn, Opelika, Dothan, Selma and southeastern Alabama) |
| 336 | North Carolina (Winston-Salem, Greensboro, North Wilkesboro, Roxboro, and northwest North Carolina) |
| 337 | Louisiana (Leesville, Lake Charles, Lafayette, New Iberia, Opelousas, De Ridder and southwestern Louisiana), split from 318 on October 11, 1999) |
| 339 | Massachusetts (Saugus, Norwood, Waltham, Woburn, east central Massachusetts and other Boston suburbs along Route 128, overlays with 781) |
| 340 | the U.S. Virgin Islands, split from 809. (all) |
| 341 | California This Area code is scheduled to provide numbering relief for Area code 510 but no date has been assigned for this to go into effect. |
| 343 | Ontario (Ottawa, eastern and southeastern Ontario) This area code is scheduled to provide numbering relief to area code 613 effective in 2011. |
| 345 | the Cayman Islands, split from 809. (all) |
| 347 | New York (New York City except Manhattan generally for mobile phones; overlays with 718 and 917) |
| 351 | Massachusetts (Fitchburg, Peabody and northeastern Massachusetts, overlays with 978) |
| 352 | Florida (Gainesville, Ocala, Inverness, Dunnellon and central Florida) |
| 360 | Washington (Bellingham, Belfair, Bremerton, Aberdeen, Olympia and western Washington except the greater Seattle area, which uses the 206, 253, and 425 area codes) |
| 361 | Texas (Corpus Christi, Victoria, George West and South Texas) |
| 364 | Kentucky west of the Pennyrile Parkway, beginning January 1, 2009. Includes Paducah; overlays with 270. |
| 369 | California This code is scheduled to provide numbering relief to Area code 707, but no date has been assigned for this to go into effect. |
| 380 | Ohio This Area code is scheduled to provide numbering relief to Area code 614 but no date has been assigned for this to go into effect. |
| 385 | Utah (Salt Lake, Utah, Davis, Weber and Morgan counties, overlays with 801), beginning mid 2008. |
| 386 | Florida (Daytona Beach, Lake City, Live Oak, Crescent City and northern and eastern Florida) |
