NumberResearchThousands-blocks in 231-721
This prefix’s ten 1,000-number blocks and who holds each — 10 on record · from the daily NANPA thousands-block report, 09/19/2026
The ten 1,000-number thousand-blocks inside prefix 231-721 and who was initially assigned each. Under pooling these blocks often belong to different carriers — the single prefix-level “assignee” is usually just the pool / code holder, not who holds the numbers. ← all 231 blocks
Most active assignees, last 30 days — NPA 231
New assignments by month
Sep 2026
Aug 2026
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Oct 2025
| Assigned | Thousands-block | Last 4 digits | Status | Assignee | OCN | Rate center | State |
|---|---|---|---|---|---|---|---|
| — | 231-721-0XXX | 0000–0999 | Reserved | 123.NET, LLC | 2550 | HART | MI |
| 2021-02-22 | 231-721-1XXX | 1000–1999 | Assigned | CELLCO PARTNERSHIP DBA VERIZON WIRELESS - MI | 6003 | HART | MI |
| 2020-10-21 | 231-721-2XXX | 2000–2999 | Assigned | ONVOY, LLCV - MI | 543C | HART | MI |
| 2020-10-21 | 231-721-3XXX | 3000–3999 | Assigned | ONVOY, LLCV - MI | 543C | HART | MI |
| — | 231-721-4XXX | 4000–4999 | Available | HART | MI | ||
| 2012-09-12 | 231-721-5XXX | 5000–5999 | Assigned | CELLCO PARTNERSHIP DBA VERIZON WIRELESS - MI | 6003 | HART | MI |
| 2021-05-20 | 231-721-6XXX | 6000–6999 | Assigned | ONVOY SPECTRUM, LLC | 624H | HART | MI |
| 2017-08-30 | 231-721-7XXX | 7000–7999 | Assigned | CENTURYLINK COMMUNICATIONS, LLC | 508J | HART | MI |
| 2026-09-14 | 231-721-8XXX | 8000–8999 | Assigned | NEW CINGULAR WIRELESS PCS, LLC - IL | 6534 | HART | MI |
| 2024-01-04 | 231-721-9XXX | 9000–9999 | Assigned | OMNIPOINT COMMUNICATIONS MIDWEST OPERATIONS, LLC | 2964 | HART | MI |
Source: NANPA Thousands Block Assignment Report (All Regions, Public), file date 09/19/2026 — Tier A primary source, refreshed on every import. Viewing is free; bulk downloads require a membership.