NumberResearch Membership · Data 09/20/2026

Recent prefix assignments

0 prefixes assigned in the last 30 days · from the daily NANPA CO code file, 09/20/2026

Full prefixes (NXX) Thousands-blocks (1,000-number pools)

The Code holder is who opened each NPA-NXX prefix — not necessarily who holds the numbers. A prefix is 10,000 numbers, but under pooling its ten 1,000-number blocks are handed out individually, often to different carriers; the code holder may hold only one block, or none. The Thousands-blocks column shows how the ten blocks are really split — click which blocks → to see who holds each 1,000-number block and its last-4-digit range. Assignments are initial assignments; the current serving carrier may differ due to portability.

Most active assignees, all time — NPA 331
T-MOBILE USA, INC. 42
New assignments by month Sep 2026 Aug 2026 Jul 2026 Jun 2026 May 2026 Apr 2026 Mar 2026 Feb 2026 Jan 2026 Dec 2025 Nov 2025 Oct 2025
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Recent NPA-NXX prefix assignments
AssignedNPA-NXXThousands-blocks taken (last-4 opening)Code holderOCNRate centerState
2022-08-12 331-289 0–9 XXXall 10 · 5 holders which blocks → T-MOBILE USA, INC. 6529 HINSDALE IL
2022-03-11 331-284 0XXX1XXX2XXX3XXX4XXX5XXX6XXX7XXX9XXX · 4 holders which blocks → T-MOBILE USA, INC. 6529 BARTLETT IL
2022-02-23 331-283 0XXX1XXX2XXX3XXX4XXX5XXX6XXX8XXX9XXX · 3 holders which blocks → T-MOBILE USA, INC. 6529 GENEVA IL
2021-08-03 331-274 0–9 XXXall 10 · 2 holders which blocks → T-MOBILE USA, INC. 6529 AURORA IL
2021-08-03 331-275 2XXX6XXX7XXX8XXX9XXX · 2 holders which blocks → T-MOBILE USA, INC. 6529 BARTLETT IL
2021-05-14 331-269 0–9 XXXall 10 · 3 holders which blocks → T-MOBILE USA, INC. 6529 AURORA IL
2021-01-14 331-268 0XXX1XXX2XXX3XXX4XXX9XXX · 4 holders which blocks → T-MOBILE USA, INC. 6529 SUGARGROVE IL
2019-06-20 331-261 0XXX1XXX3XXX4XXX5XXX6XXX9XXX · 5 holders which blocks → T-MOBILE USA, INC. 6529 LEMONT IL
2018-10-19 331-242 0–9 XXXwhole prefix which blocks → T-MOBILE USA, INC. 6529 LOMBARD IL
2018-10-19 331-243 0–9 XXXall 10 · 2 holders which blocks → T-MOBILE USA, INC. 6529 LOMBARD IL
2018-10-19 331-246 0–9 XXXall 10 · 2 holders which blocks → T-MOBILE USA, INC. 6529 LEMONT IL
2017-04-05 331-230 0–9 XXXall 10 · 3 holders which blocks → T-MOBILE USA, INC. 6529 AURORA IL
2017-04-05 331-236 0–9 XXXall 10 · 5 holders which blocks → T-MOBILE USA, INC. 6529 WHEATON IL
2017-03-20 331-226 0–9 XXXall 10 · 4 holders which blocks → T-MOBILE USA, INC. 6529 NAPERVILLE IL
2016-08-23 331-707 0XXX2XXX3XXX4XXX5XXX6XXX7XXX8XXX9XXX · 5 holders which blocks → T-MOBILE USA, INC. 6529 AURORA IL
2016-07-13 331-757 0–9 XXXall 10 · 7 holders which blocks → T-MOBILE USA, INC. 6529 LEMONT IL
2016-03-17 331-300 0–9 XXXall 10 · 7 holders which blocks → T-MOBILE USA, INC. 6529 AURORA IL
2015-07-20 331-321 0–9 XXXall 10 · 4 holders which blocks → T-MOBILE USA, INC. 6529 AURORA IL
2015-06-25 331-814 0–9 XXXall 10 · 6 holders which blocks → T-MOBILE USA, INC. 6529 NAPERVILLE IL
2015-02-20 331-304 0–9 XXXall 10 · 3 holders which blocks → T-MOBILE USA, INC. 6529 BARTLETT IL
2014-10-27 331-253 0–9 XXXall 10 · 4 holders which blocks → T-MOBILE USA, INC. 6529 LEMONT IL
2014-10-13 331-307 0–9 XXXall 10 · 4 holders which blocks → T-MOBILE USA, INC. 6529 LOMBARD IL
2014-10-13 331-980 0–9 XXXwhole prefix which blocks → T-MOBILE USA, INC. 6529 AURORA IL
2014-07-16 331-254 0–9 XXXall 10 · 5 holders which blocks → T-MOBILE USA, INC. 6529 SUGARGROVE IL
2013-10-24 331-703 0–9 XXXall 10 · 4 holders which blocks → T-MOBILE USA, INC. 6529 W CHICAGO IL
2013-07-09 331-218 0–9 XXXall 10 · 3 holders which blocks → T-MOBILE USA, INC. 6529 WHEATON IL
2013-04-18 331-245 0–9 XXXall 10 · 3 holders which blocks → T-MOBILE USA, INC. 6529 BARTLETT IL
2012-04-10 331-250 0–9 XXXall 10 · 2 holders which blocks → T-MOBILE USA, INC. 6529 AURORA IL
2012-01-17 331-202 0XXX1XXX2XXX3XXX4XXX5XXX6XXX7XXX8XXX · 3 holders which blocks → T-MOBILE USA, INC. 6529 ELMHURST IL
2011-10-21 331-205 0–9 XXXall 10 · 3 holders which blocks → T-MOBILE USA, INC. 6529 AURORA IL
2011-10-12 331-203 0–9 XXXall 10 · 2 holders which blocks → T-MOBILE USA, INC. 6529 AURORA IL
2011-10-12 331-206 0XXX1XXX9XXX · 3 holders which blocks → T-MOBILE USA, INC. 6529 AURORA IL
2011-08-22 331-225 0XXX1XXX2XXX3XXX4XXX5XXX6XXX8XXX9XXX · 4 holders which blocks → T-MOBILE USA, INC. 6529 ELMHURST IL
2011-07-12 331-220 0–9 XXXall 10 · 3 holders which blocks → T-MOBILE USA, INC. 6529 AURORA IL
2011-07-11 331-200 0–9 XXXall 10 · 6 holders which blocks → T-MOBILE USA, INC. 6529 BARTLETT IL
2008-11-18 331-826 0XXX1XXX2XXX3XXX4XXX8XXX9XXX · 4 holders which blocks → T-MOBILE USA, INC. 6529 ELMHURST IL
2008-10-22 331-472 0–9 XXXall 10 · 7 holders which blocks → T-MOBILE USA, INC. 6529 NAPERVILLE IL
2008-07-30 331-262 0XXX1XXX2XXX3XXX4XXX5XXX7XXX8XXX9XXX · 3 holders which blocks → T-MOBILE USA, INC. 6529 AURORA IL
2007-11-05 331-645 0–9 XXXwhole prefix which blocks → T-MOBILE USA, INC. 6529 ELMHURST IL
2007-09-18 331-575 0–9 XXXall 10 · 2 holders which blocks → T-MOBILE USA, INC. 6529 AURORA IL
2007-09-18 331-643 0–9 XXXall 10 · 2 holders which blocks → T-MOBILE USA, INC. 6529 AURORA IL
2007-07-11 331-425 0–9 XXXall 10 · 3 holders which blocks → T-MOBILE USA, INC. 6529 AURORA IL

Source: NANPA CO Code Assignments (Utilized, All States, Public), file date 09/20/2026 — Tier A primary source, refreshed on every import. Viewing is free; bulk downloads require a membership.