Spam Calling Control & Call Verification

Unwanted and automated phone calls are an unfortunate reality for every business today. Advances in caller ID spoofing, robocalls, and AI-driven dialing mean that even well-managed phone systems are constantly being targeted.

At DTPBX, we have options to control these calls so that real people can still reach you, while automated and abusive calls are reduced. These controls are not implemented by default - we do so when we become aware of impacts to our customers. This is so that we don't impact real callers without your knowledge.

This article explains what we do, why it works, and what decisions we’ll ask you to make.

What problem are we solving?

Spam calls fall into a few broad categories:

  • Robocalls and prerecorded messages
  • Scam calls impersonating legitimate businesses or numbers
  • Automated “dialers” probing systems for valid phone numbers
  • AI-assisted calling systems that sound human but are not

Modern phone networks allow callers to present almost any caller ID they want, which makes it difficult to block spam based on phone number alone.

This is also why we do not recommend explicit number blocking as a spam control method - it doesn't work because spam callers rotate numbers.

The industry’s answer to this problem is call attestation.

What is call attestation?

Call attestation is part of a telecom framework called STIR/SHAKEN. It allows phone carriers to cryptographically verify how confident they are that a caller is legitimate.

You don’t need to remember the acronym — just the idea:

Attestation tells us how trustworthy the caller’s identity is.

There are three common levels:

A-Level Attestation (Highest confidence)

  • The caller’s carrier knows who is calling
  • The caller is authorized to use that phone number
  • These calls are very likely legitimate

B-Level Attestation (Medium confidence)

  • The carrier knows who is calling
  • But cannot fully confirm they’re authorized to use that number
  • Often seen with business systems, older carriers, or complex call routing

C-Level Attestation (Lowest confidence)

  • The carrier cannot verify the caller
  • Often associated with spoofed numbers or high-risk traffic
  • Legitimate callers can still show up as C in some cases

Important note:
Even legitimate businesses — including your own staff calling from certain phones or systems — may occasionally appear as B or even C attestation. This is more common than most people expect.

How we use attestation to protect your phone system

Rather than simply blocking calls, we use call interruption and verification.

Depending on your chosen settings:

  • High-confidence calls (A-level) may ring through normally
  • Lower-confidence calls (B or C) may be briefly interrupted by a verification prompt
  • The caller hears a short message asking them to press a key to continue
  • If they confirm, the call is connected as usual

What this means for real callers

  • Calls are not silently dropped
  • A genuine human can still reach you
  • The extra step typically takes only a few seconds

What this means for spam calls

  • Automated dialers usually fail
  • Prerecorded messages can’t respond
  • Many AI-driven spam systems disconnect immediately

“Are we going to miss important calls?”

This is the most common concern — and a valid one.

Our approach is designed specifically to avoid losing legitimate calls:

  • Calls aren’t blocked outright
  • They’re temporarily paused and verified
  • Humans can still get through
  • You can choose how strict the filtering is

No system is perfect, and we want to be transparent:

  • Very advanced AI calling systems may eventually learn to pass simple verification
  • Some legitimate callers may find the extra step mildly inconvenient
  • That’s why you choose the level of protection, not us

Choosing your protection level

This is the key decision we’ll ask you to make.

Option 1: Filter only C-level calls

  • Least disruptive
  • Allows most calls through
  • Some spam will still ring your phones

Option 2: Filter B- and C-level calls (most common and our default recommendation)

  • Strong reduction in spam
  • Some impact on real callers
  • Recommended for most offices

We’ll help you understand what your inbound traffic looks like and recommend a starting point — but the final decision is always yours.

Why this approach works better than blocking

Traditional “block lists” and number-based filtering don’t work well anymore. Spam callers constantly rotate numbers and spoof legitimate caller IDs.

Verification-based controls focus on behavior, not just numbers.

That’s why this method:

  • Stops more unwanted calls
  • Avoids false positives
  • Gives humans a second chance to connect

Our goal

Our goal is simple:

Protect your staff from unnecessary interruptions while ensuring real people can still reach you.

Spam calling technology will continue to evolve. We actively monitor trends and adjust our controls as needed.

If you’d like to implement, review, or change your call verification settings, just let us know.