NumberResearchThousands-blocks in 517-921
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 517-921 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 517 blocks
Most active assignees, all time — NPA 517
New assignments by month
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Oct 2025
| Assigned | Thousands-block | Last 4 digits | Status | Assignee | OCN | Rate center | State |
|---|---|---|---|---|---|---|---|
| 2020-01-15 | 517-921-0XXX | 0000–0999 | Assigned | ONVOY, LLCV - MI | 543C | ADDISON | MI |
| 2020-01-15 | 517-921-1XXX | 1000–1999 | Assigned | ONVOY, LLCV - MI | 543C | ADDISON | MI |
| — | 517-921-2XXX | 2000–2999 | Reserved | ACD TELECOM, INC. - MI | 3535 | ADDISON | MI |
| — | 517-921-3XXX | 3000–3999 | Reserved | ACD TELECOM, INC. - MI | 3535 | ADDISON | MI |
| — | 517-921-4XXX | 4000–4999 | Reserved | ACD TELECOM, INC. - MI | 3535 | ADDISON | MI |
| 2018-04-24 | 517-921-5XXX | 5000–5999 | Assigned | LEVEL 3 COMMUNICATIONS, LLC - MI | 6120 | ADDISON | MI |
| 2015-12-03 | 517-921-6XXX | 6000–6999 | Assigned | CENTURYLINK COMMUNICATIONS, LLC | 508J | ADDISON | MI |
| — | 517-921-7XXX | 7000–7999 | Reserved | ACD TELECOM, INC. - MI | 3535 | ADDISON | MI |
| 2009-08-27 | 517-921-8XXX | 8000–8999 | Assigned | NEW CINGULAR WIRELESS PCS, LLC - IL | 6534 | ADDISON | MI |
| — | 517-921-9XXX | 9000–9999 | Reserved | ACD TELECOM, INC. - MI | 3535 | ADDISON | 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.