Th first 2 digits city/state codes the next 4 are USOC circuit type codes the last part is a database number that the LEC uses and reuses when they assign circuits. When you call in trouble or repair they use the last number to search for the account and then use the USOC code to determine what type of service it is and the city/state code to send the trouble to the correct repair center. You can tell how old a circuit is by how low the database number is.