Business Telecom Systems: A Guide to Choosing the Best Technologies and Services

(subject to change)
| 201 | New Jersey, NE |
| 202 | District of Columbia |
| 203 | Connecticut, SW |
| 204 | Manitoba |
| 205 | Alabama, northern |
| 206 | Washington, Seattle area |
| 207 | Maine |
| 208 | Idaho |
| 209 | California, N central |
| 210 | Texas, San Antonio area |
| 212 | New York, Manhattan |
| 213 | California, Los Angeles |
| 214 | Texas, Dallas |
| 215 | Pennsylvania, Philadelphia |
| 216 | Ohio, Cleveland, NE |
| 217 | Illinois, central |
| 218 | Minnesota, northern |
| 219 | Indiana, northern |
| 224 | Illinois, far NE, Chicago |
| 225 | Louisiana, central eastern |
| 228 | Mississippi, SE |
| 231 | Michigan |
| 240 | Maryland, western and southern |
| 242 | Bahamas |
| 246 | Barbados |
| 248 | Michigan, Oakland County |
| 250 | British Columbia, all except Vancouver |
| 252 | North Carolina, NE |
| 253 | Washington, Tacoma and S Seattle |
| 254 | Texas, N central |
| 256 | Alabama, northern except Birmingham |
| 264 | Anguilla |
| 267 | Pennsylvania, SE |
| 268 | Antigua and Barbuda |
| 281 | Texas, suburban Houston |
| 284 | British Virgin Islands |
| 301 | Maryland, NW |
| 302 | Delaware |
| 303 | Colorado, Denver area |
| 304 | West Virginia |
| 305 | Florida, SW including Miami |
| 306 | Saskatchewan |
| 307 | Wyoming |
| 308 | Nebraska, western |
| 309 | Illinois, upper NW |
| 310 | California, Santa Monica area |
| 312 | Illinois, Chicago |
| 313 | Michigan, Detroit area |
| 314 | Missouri, St Louis area |
| 315 | New York, Syracuse and N central NY |
| 316 | Kansas, southern |
| 317 | Indiana, Indianapolis area |
| 318 | Louisiana, western and northern |
| 319 | Iowa, eastern |
| 320 | Minnesota, central except Minneapolis |
| 323 | California, around central Los Angeles |
| 330 | Ohio, central NE |
| 334 | Alabama, southern |
| 336 | North Carolina, NW |
| 340 | US Virgin Islands |
| 345 | Cayman Islands |
| 352 | Florida, NW central |
| 360 | Washington, western except Seattle |
| 401 | Rhode Island |
| 402 | Nebraska, eastern |
| 403 | Alberta, southern |