NumberResearchThousands-blocks in 520-737
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 520-737 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 520 blocks
Most active assignees, all time — NPA 520
New assignments by month
Sep 2026
Aug 2026
Jul 2026
Jun 2026
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Oct 2025
| Assigned | Thousands-block | Last 4 digits | Status | Assignee | OCN | Rate center | State |
|---|---|---|---|---|---|---|---|
| — | 520-737-0XXX | 0000–0999 | Available | SIERRAVIST | AZ | ||
| — | 520-737-1XXX | 1000–1999 | Available | SIERRAVIST | AZ | ||
| — | 520-737-2XXX | 2000–2999 | Available | SIERRAVIST | AZ | ||
| — | 520-737-3XXX | 3000–3999 | Available | SIERRAVIST | AZ | ||
| 2025-10-03 | 520-737-4XXX | 4000–4999 | Assigned | HD CARRIER LLC | 321J | SIERRAVIST | AZ |
| 2024-06-17 | 520-737-5XXX | 5000–5999 | Assigned | ALLO COMMUNICATIONS LLC | 907K | SIERRAVIST | AZ |
| 2025-10-03 | 520-737-6XXX | 6000–6999 | Assigned | HD CARRIER LLC | 321J | SIERRAVIST | AZ |
| 2025-10-03 | 520-737-7XXX | 7000–7999 | Assigned | HD CARRIER LLC | 321J | SIERRAVIST | AZ |
| 2025-10-03 | 520-737-8XXX | 8000–8999 | Assigned | HD CARRIER LLC | 321J | SIERRAVIST | AZ |
| 2025-10-03 | 520-737-9XXX | 9000–9999 | Assigned | HD CARRIER LLC | 321J | SIERRAVIST | AZ |
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.