NumberResearchThousands-blocks in 303-353
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 303-353 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 303 blocks
Most active assignees, all time — NPA 303
New assignments by month
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Oct 2025
| Assigned | Thousands-block | Last 4 digits | Status | Assignee | OCN | Rate center | State |
|---|---|---|---|---|---|---|---|
| 2006-01-03 | 303-353-0XXX | 0000–0999 | Assigned | ONVOY, LLC - CO | 026D | DENVER | CO |
| 2007-02-08 | 303-353-1XXX | 1000–1999 | Assigned | ONVOY, LLC - CO | 026D | DENVER | CO |
| 2001-06-19 | 303-353-2XXX | 2000–2999 | Assigned | COMCAST IP PHONE, LLC | 318J | DENVER | CO |
| 2001-06-19 | 303-353-3XXX | 3000–3999 | Assigned | TELEPORT COMMUNICATIONS AMERICA, LLC - CO | 7378 | DENVER | CO |
| 2001-06-19 | 303-353-4XXX | 4000–4999 | Assigned | COMCAST IP PHONE, LLC | 318J | DENVER | CO |
| 2002-01-15 | 303-353-5XXX | 5000–5999 | Assigned | TELEPORT COMMUNICATIONS AMERICA, LLC - CO | 7378 | DENVER | CO |
| 2002-01-15 | 303-353-6XXX | 6000–6999 | Assigned | COMCAST IP PHONE, LLC | 318J | DENVER | CO |
| 2002-01-15 | 303-353-7XXX | 7000–7999 | Assigned | TELEPORT COMMUNICATIONS AMERICA, LLC - CO | 7378 | DENVER | CO |
| — | 303-353-8XXX | 8000–8999 | Reserved | COMCAST IP PHONE, LLC | 318J | DENVER | CO |
| 2007-01-11 | 303-353-9XXX | 9000–9999 | Assigned | COMCAST IP PHONE, LLC | 318J | DENVER | CO |
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.