NumberResearchThousands-blocks in 231-237
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 231-237 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, all time — NPA 231
New assignments by month
Sep 2026
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Oct 2025
| Assigned | Thousands-block | Last 4 digits | Status | Assignee | OCN | Rate center | State |
|---|---|---|---|---|---|---|---|
| — | 231-237-0XXX | 0000–0999 | Reserved | MICHIGAN BELL TEL CO | 9323 | CHARLEVOIX | MI |
| — | 231-237-1XXX | 1000–1999 | Reserved | MICHIGAN BELL TEL CO | 9323 | CHARLEVOIX | MI |
| 2012-05-04 | 231-237-2XXX | 2000–2999 | Assigned | ONVOY, LLCV - MI | 543C | CHARLEVOIX | MI |
| 2004-09-24 | 231-237-3XXX | 3000–3999 | Assigned | ACD TELECOM, INC. - MI | 3535 | CHARLEVOIX | MI |
| 2004-10-20 | 231-237-4XXX | 4000–4999 | Assigned | LEVEL 3 COMMUNICATIONS, LLC - MI | 6120 | CHARLEVOIX | MI |
| 2007-02-08 | 231-237-5XXX | 5000–5999 | Assigned | LEVEL 3 COMMUNICATIONS, LLC - MI | 6120 | CHARLEVOIX | MI |
| 2015-08-12 | 231-237-6XXX | 6000–6999 | Assigned | CENTURYLINK COMMUNICATIONS, LLC | 508J | CHARLEVOIX | MI |
| 2015-11-23 | 231-237-7XXX | 7000–7999 | Assigned | PEERLESS NETWORK OF MICHIGAN, LLC - MI | 933G | CHARLEVOIX | MI |
| 2018-05-22 | 231-237-8XXX | 8000–8999 | Assigned | BANDWIDTH.COM CLEC, LLC - MI | 991E | CHARLEVOIX | MI |
| — | 231-237-9XXX | 9000–9999 | Reserved | MICHIGAN BELL TEL CO | 9323 | CHARLEVOIX | 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.