CO Codes/Thousands-Blocks
A Central Office (CO) code or NXX refers to the second three digits (also called digits D-E-F) of a ten-digit telephone number in the form of NPA-NXX-XXXX, where N represents any one of the numbers 2 through 9 and X represents any one of the numbers 0 through 9. CO codes are also known as an exchange, or prefix, or an NXX.
A thousands-block refers a range of one thousand telephone numbers (TN) within a CO code (NPA-NXX) beginning with X000 and ending with X999, where X is a value from 0 to 9.
NANPA assigns CO codes in the U.S. and U.S. territories and thousands-blocks in the U.S. and U.S. territories where thousands-block pooling is implemented.
The following Company Code Category types may request numbering resources directly from NANPA:
- Incumbent Local Exchange Carrier ILEC
- Regional Bell Operating Company RBOC
- Competitive Local Exchange Carrier CLEC
- Personal Communications Service PCS
- Unbundled Local Exchange Carrier ULEC
- Wireless Carriers WIRE
- Internet Provider Enabled Services IPES (Interconnected VoIP)
To assist new service providers, NANPA recommends reviewing the New Service Provider Check List prior to requesting CO codes and thousands-blocks.
To assist Interconnected VoIP Providers, NANPA recommends reviewing Getting Started for new Interconnected VoIP Providers and 30-Day Notification Regulatory Contact and Information prior to requesting CO codes and thousands-blocks.
To assist service providers that require a state waiver, refer to the State Waiver/Safety Valve Process and Regulatory Contacts matrix.
The Evidence of State Certification identifies what each state regulatory authority provides as evidence of certification to provide service in the area where initial numbering resources are being requested by service providers that are categorized as a CLEC, ILEC, RBOC, or ULEC.
NAS user guides and templates may be found under Resources.
CO Code Jeopardy Procedures
When NANPA declares extraordinary jeopardy in an NPA indicating that the supply of CO codes may exhaust before NPA relief can be provided, standard interim jeopardy procedures will take effect immediately.
Interim procedures will remain in effect until the industry develops the "final" jeopardy procedures specific to the NPA. NANPA will post the interim jeopardy procedures within one week after declaring jeopardy.
No later than three weeks after jeopardy is declared, the industry will meet to develop final jeopardy procedures. These procedures will limit the number of CO codes that can be assigned each month. NANPA will post the final jeopardy procedures within two weeks after the industry reaches consensus on the final procedures. CO code holders should monitor the list below and adjust their applications per the jeopardy procedures.
NPA(s) in Jeopardy
| State | Jeopardy | Date Jeopardy Declared | Date Jeopardy Procedures Published or Revised | Jeopardy Procedures |
*Currently there are no NPA(s) in Jeopardy.