I have a virtual office for my business. As part of their VO services, they offer a telephone number service that is a VOIP thing... requires me to put an App on my smartphone and then I can get calls through that app.

Well, I already have a phone number that I got through my regular cell carrier. Today, I called the virtual office company and asked them if I could port my existing number to their service. the guy on the phone told me "oh, it looks like this is a Tier 0 number, so we can port it no problem"

So, then I asked the robot about what these Tier numbers are all about. Here's the robot's output in raw.... hope it's helpful:

In common telecom & caller-ID reputation contexts, phone number “tiers” don’t refer to the digits themselves but to how the number, the network it’s on, or the service associated with it is classified, often affecting trust, call delivery, and spam labeling. The specific meaning of Tier 0–3 depends on the framework being used—but two broad interpretations are typical:

1) Carrier / Network Tiers (Indirectly affecting phone numbers)1) Carrier / Network Tiers (Indirectly affecting phone numbers)

This isn’t a classification of the number itself but of the network/provider responsible for routing it. Larger carriers are considered higher “tier”:

• Tier 1 carriers — Global backbone operators with their own extensive networks (e.g., AT&T, Verizon). They don’t need to pay other networks to reach the whole Internet/telephony ecosystem. Tier 1 status often correlates with better caller ID propagation and reputation handling because of direct infrastructure and peering. ([thousandeyes.com][1])
• Tier 2 carriers — Regional/national operators with some peering but still pay for transit on parts of the network. ([thousandeyes.com][1])
• Tier 3 carriers — Local/mobile resellers or smaller networks that rely entirely on upstream transit from other carriers. ([thousandeyes.com][1])

In practice, a number issued on a Tier 1 network may be less likely to be misclassified or have caller ID issues than one on a Tier 3 network, but this is about infrastructure and routing, not a numeric property of the number itself.

2) Reputation / Service Tiers for Phone Numbers (e.g., spam/legitimacy scoring)2) Reputation / Service Tiers for Phone Numbers (e.g., spam/legitimacy scoring)

In caller-ID and number reputation systems used by carriers and analytics platforms, Tier 0–3 might refer to the level of validation, trust, or labeling applied to a phone number’s calling behavior. Unlike carrier tiers, this classification isn’t standardized industry-wide, but in some reputation systems you’ll see a tiered risk categorization roughly like this:

• Tier 0 – Clean / trusted / fully authenticated numbers
  • The call is validated by authentication frameworks (like STIR/SHAKEN in the U.S.) and shows a verified caller ID.
  • These numbers have a strong reputation score with minimal risk indicators.
• Tier 1 – Low-risk/primary business numbers
  • Typically legitimate businesses with good usage patterns, low complaint rates, and consistent caller ID information.
  • Not flagged by carriers or third-party databases.
• Tier 2 – Moderate risk / unverified or mixed-use numbers
  • May lack full authentication or show some patterns (e.g., higher volume, unfamiliar to carriers) that raise mild suspicion.
  • Potential for flags like “Potential Spam” depending on behavior.
• Tier 3 – High-risk / flagged numbers
  • Strong indicators of unwanted or abusive calling behavior (spam, scam, fraud) either via carrier algorithms, third-party lists, or user reports.
  • Calls from these numbers are most likely to be blocked or labeled “Spam Likely,” “Scam Risk,” etc. ([NobelBiz][2])

These tiers act like a reputation ladder (similar to a credit score): lower tier = better trust & delivery; higher numerical tier = greater suspicion or filtering applied.

Why this mattersWhy this matters

• Caller ID display: A number in Tier 0–1 is more likely to show accurate caller ID and reach recipients without spam flags.
• Blocking & labeling: Tier 2–3 numbers are more susceptible to algorithmic flags or automated blocks by carriers and consumer apps.
• Outbound success: Businesses monitor and improve reputation tiers to increase answer rates and avoid spam labels. ([callblitz.com][3])

Short conceptual summaryShort conceptual summary

Carrier tiers (1–3) classify the network/provider behind the phone number, with Tier 1 being the most foundational.

Phone number reputation tiers (0–3) classify the trustworthiness or risk of the number’s calling behavior, with Tier 0 cleanest and Tier 3 riskiest. These reputation tiers affect how calls are displayed and whether they’re blocked or labeled as spam. (

[kixie.com][4]

If you’re thinking specifically about reputation scoring tiers used by analytics/labeling systems (Spam Risk, Scam Likely, etc.), let me know and I can map those onto this Tier 0–3 model with examples.

[1]: https://www.thousandeyes.com/learning/techtorials/isp-tiers?utm_source=chatgpt.com "Internet Service Provider 3-Tier Model"

[2]: https://nobelbiz.com/blog/how-to-avoid-getting-your-number-labeled-as-spam/?utm_source=chatgpt.com "A Guide to Call Blocking and Labeling, and Phone Number ..."

[3]: https://callblitz.com/blog/10-ways-to-manage-your-caller-id-reputation?utm_source=chatgpt.com "10 Ways to Manage Your Caller ID Reputation"

[4]: https://www.kixie.com/sales-blog/caller-id-reputation-what-it-is-why-it-matters-and-how-to-monitor-it/?utm_source=chatgpt.com "Caller ID Reputation: What It Is, Why It Matters, and How to ..."