Industry guidelines allow for the voluntary transfer of an over-contaminated Thousands-Block from one service provider to another.  This process is slightly different from the normal return of a Thousands-Block with ten percent or less contamination back to the numbering pool. 

The voluntary transfer of an over-contaminated block allows a service provider with sufficient numbering resources to help minimize the need for additional Thousands-Blocks or Central Office Codes to be utilized by voluntarily transferring an over-contaminated block with greater than ten percent numbers in use to another service provider in need of numbering resources in a specific rate center.  

Section 9.1.9 of the ATIS Thousands-Block (NPA-NXX-X) & Central Office Code (NPA-NXX) Administration Guidelines (published on behalf of the Industry Numbering Committee) outlines this process, which can be found by going to:

A snapshot of the relevant rules from September 23, 2022 can also be found here:

9.1.9 Thousands-Block Transfer Process

For Thousands-Blocks not involved in a merger, acquisition, or Type 1 Interconnection Service Provider to Type 2 Interconnection Service Provider migration, SPs shall provide a letter or email from the relinquishing Service Provider indicating:

a) The reason for the transfer (i.e., TNs are assigned and/or reserved for a single customer),

b) The Thousands-Block(s) being transferred, and

c) Confirming that the Thousands-Block(s) is in use with active customers.

d) Confirm that the Thousands-Block(s) is over 10% contamination.

All Thousands-Block transfers shall be mutually agreed to by both the relinquishing and receiving SP.

The Thousands-Block Applicant (SP receiving the Thousands-Block to be transferred) shall submit a complete Part 1A Thousands-Block (NPA-NXX-X) Application and Part 1B NPAC Thousands-Block Data. In addition, the Applicant requesting the Thousands-Block transfer shall also provide:

a) For a merger/acquisition, SPs shall provide documentation of the merger/acquisition with the request.
b) For all other transfers, the SP requesting the transfer shall provide an email or letter from the current Thousands-Block Holder indicating the NPA-NXX-X, reason for the transfer, and a confirmation that there are active customers and that the block is over ten percent contaminated. The PA shall ensure that the transfer is mutually acceptable.

The PA shall notify the recipient SP when the Thousands-Block record has been successfully modified in BIRRDS. It is the responsibility of the SP receiving the Thousands-Block to enter, or arrange for the entry of, any changes to BIRRDS data (e.g., Switching Entity/POI) associated with the transfer of the Thousands-Block.

If the Thousands-Block being transferred shall be the Initial Block for the Rate Center, the SP shall ensure that it satisfies the license and/or Certification requirements and facilities readiness requirements (see Section 4.8) and provide the appropriate documentation with the transfer request.

All time intervals applicable to the assignment of a new Thousands-Block apply in the case of a Thousands-Block transfer. These intervals do not address the time intervals needed to perform the network and other rearrangements associated with the Thousands-Block transfer.

Upon approval of the request, the PA shall modify the Thousands-Block record in BIRRDS for the Thousands-Block to be transferred to reflect the OCN, Effective Date and Switching Entity/POI of the SP to which the Thousands-Block shall be transferred. To the extent necessary, the PA shall coordinate the change with TRA.

If a Part 4A Confirmation of Thousands-Block in Service is not on file for the Thousands-Block that is being transferred, and the Part 4A due date has passed, then the PA shall deny the request to transfer the Thousands-Block until a Part 4A is received from the appropriate regulatory authority.

The resulting SP in a merger/acquisition shall revise and provide a new, consolidated forecast for Numbering Resources. The Thousands-Block Holder of a Thousands-Block Assigned by the PA or acquired by other means such as transfer (e.g., by merger or acquisition) shall use the Thousands-Block consistent with these guidelines. Additionally, the new Thousands-Block Holder shall participate in an Audit process, as necessary.