NumberResearchThousands-blocks in 858-436
This prefix’s ten 1,000-number blocks and who holds each — 10 on record · from the daily NANPA thousands-block report, 09/20/2026
The ten 1,000-number thousand-blocks inside prefix 858-436 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 858 blocks
Most active assignees, all time — NPA 858
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| Assigned | Thousands-block | Last 4 digits | Status | Assignee | OCN | Rate center | State |
|---|---|---|---|---|---|---|---|
| — | 858-436-0XXX | 0000–0999 | Reserved | U.S. TELEPACIFIC CORP. DBA TPX COMMUNICATIONS | 671J | DEL MAR | CA |
| — | 858-436-1XXX | 1000–1999 | Reserved | U.S. TELEPACIFIC CORP. DBA TPX COMMUNICATIONS | 671J | DEL MAR | CA |
| — | 858-436-2XXX | 2000–2999 | Reserved | U.S. TELEPACIFIC CORP. DBA TPX COMMUNICATIONS | 671J | DEL MAR | CA |
| — | 858-436-3XXX | 3000–3999 | Reserved | U.S. TELEPACIFIC CORP. DBA TPX COMMUNICATIONS | 671J | DEL MAR | CA |
| 2006-03-07 | 858-436-4XXX | 4000–4999 | Assigned | T-MOBILE USA, INC. | 6529 | DEL MAR | CA |
| 2007-03-30 | 858-436-5XXX | 5000–5999 | Assigned | T-MOBILE USA, INC. | 6529 | DEL MAR | CA |
| 2007-06-21 | 858-436-6XXX | 6000–6999 | Assigned | T-MOBILE USA, INC. | 6529 | DEL MAR | CA |
| 2007-07-17 | 858-436-7XXX | 7000–7999 | Assigned | COMCAST PHONE OF CALIFORNIA, LLC | 394L | DEL MAR | CA |
| — | 858-436-8XXX | 8000–8999 | Reserved | U.S. TELEPACIFIC CORP. DBA TPX COMMUNICATIONS | 671J | DEL MAR | CA |
| — | 858-436-9XXX | 9000–9999 | Reserved | U.S. TELEPACIFIC CORP. DBA TPX COMMUNICATIONS | 671J | DEL MAR | CA |
Source: NANPA Thousands Block Assignment Report (All Regions, Public), file date 09/20/2026 — Tier A primary source, refreshed on every import. Viewing is free; bulk downloads require a membership.