NumberingData
Verified Nov 1, 2026 · Source: NANPA CO Code Assignment Records

NICASIO prefixes in area code 628

NANPA records 5 assigned NXX blocks to rate center NICASIO in area code 628, 2.6% of the 193 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. 3 holders hold those blocks, the largest being T-MOBILE USA, INC. (2), FRACTEL, LLC (2), COMMIO, LLC (1). The earliest assignment on record here is 2016-07-01 and the most recent 2023-08-09. 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 code 415 – overlay codes cover the same geography, so a rate center is served by all of them.

5 assigned blocks – 2.6% of 628
3 holders of record
5 of them pooled in 1,000-number lots

Prefixes assigned here

PrefixHolder of recordAssignedPooledIn service
628-204 T-Mobile T-MOBILE USA, INC. 2016-07-01 yes yes
628-258 T-Mobile T-MOBILE USA, INC. 2017-10-19 yes yes
628-293 COMMIO, LLC 2023-08-09 yes yes
628-356 FRACTEL, LLC 2019-11-22 yes yes
628-577 FRACTEL, LLC 2021-07-15 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

HolderBrandBlocksShare here
T-MOBILE USA, INC. T-Mobile 2 40%
FRACTEL, LLC – 2 40%
COMMIO, LLC – 1 20%

Same rate center in other codes

Overlay codes cover the same geography, so one rate center is served by all of them.

Frequently asked

Which prefixes belong to NICASIO in area code 628?

5 blocks: 204, 258, 293, 356, 577. The table above gives the holder of each.

Which carriers have numbers in NICASIO?

T-MOBILE USA, INC. (2 blocks), FRACTEL, LLC (2 blocks), COMMIO, LLC (1 block). These are the holders on record; the carrier actually serving a given number can differ, because numbers move with their owners.

Is NICASIO 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.

Other rate centers in 628

All 193 prefixes in 628