CASTLEROCK prefixes in area code 928
NANPA records 5 assigned NXX blocks to rate center CASTLEROCK in area code 928, 0.8% of the 637 blocks assigned in the code. A rate center is the billing geography a block is allocated to – NANPA truncates the name to ten characters, so read it as a NANPA label rather than a town. 5 holders hold those blocks, the largest being CELLCO PARTNERSHIP DBA VERIZON WIRELESS - AZ (1), ONVOY, LLC - AZ (1), LEVEL 3 COMMUNICATIONS, LLC - AZ (1). The earliest assignment on record here is 2005-03-02 and the most recent 2025-09-25. 5 of them are in thousands-block pooling, so those prefixes are shared between carriers in 1,000-number lots. The same rate center name also appears in area codes 360, 564 – overlay codes cover the same geography, so a rate center is served by all of them.
Prefixes assigned here
| Prefix | Holder of record | Assigned | Pooled | In service |
|---|---|---|---|---|
| 928-265 | Verizon CELLCO PARTNERSHIP DBA VERIZON WIRELESS - AZ | 2025-09-25 | yes | yes |
| 928-397 | Onvoy ONVOY, LLC - AZ | 2020-12-23 | yes | yes |
| 928-466 | Lumen LEVEL 3 COMMUNICATIONS, LLC - AZ | 2005-03-02 | yes | yes |
| 928-544 | FRACTEL, LLC | 2020-06-02 | yes | yes |
| 928-764 | Frontier CITIZENS UTILITIES RURAL DBA FRONTIER UT RURAL | – | yes | yes |
The holder is who received the block from the numbering administrator. It is not necessarily the carrier serving a given number: numbers move with their owners, and a pooled block is shared.
Who holds the blocks
| Holder | Brand | Blocks | Share here |
|---|---|---|---|
| CELLCO PARTNERSHIP DBA VERIZON WIRELESS - AZ | Verizon | 1 | 20% |
| ONVOY, LLC - AZ | Onvoy | 1 | 20% |
| LEVEL 3 COMMUNICATIONS, LLC - AZ | Lumen | 1 | 20% |
| FRACTEL, LLC | – | 1 | 20% |
| CITIZENS UTILITIES RURAL DBA FRONTIER UT RURAL | Frontier | 1 | 20% |
Frequently asked
Which prefixes belong to CASTLEROCK in area code 928?
5 blocks: 265, 397, 466, 544, 764. The table above gives the holder of each.
Which carriers have numbers in CASTLEROCK?
CELLCO PARTNERSHIP DBA VERIZON WIRELESS - AZ (1 block), ONVOY, LLC - AZ (1 block), LEVEL 3 COMMUNICATIONS, LLC - AZ (1 block), FRACTEL, LLC (1 block), CITIZENS UTILITIES RURAL DBA FRONTIER UT RURAL (1 block). These are the holders on record; the carrier actually serving a given number can differ, because numbers move with their owners.
Is CASTLEROCK a city?
It is a rate center – the unit NANPA allocates number blocks to. Its name is abbreviated to ten characters and is not necessarily a settlement: we print it as recorded rather than guess at the full name.