A 487 SIP error means your call was terminated at the carrier layer before it ever reached a device. No ring. No voicemail. Nothing. And in most outbound operations, it never shows up as a problem.

That's where the revenue leak lives.

What the 487 Code Actually Means

SIP — Session Initiation Protocol — is the signaling language that voice networks use to set up and tear down calls. When you dial out, your system sends an INVITE to the carrier network. The carrier responds with a series of codes telling you what happened.

A 200 OK means the call connected at the network layer. A 486 means the line was busy. A 404 means the number doesn't exist.

A 487 — "Request Terminated" — means the call was cancelled or killed before it completed. The session never established. In many cases, this happens because the carrier or an analytics provider flagged your number and refused to complete the call silently.

The call looks like it went out. Your dialer may log it as an attempt. But a human never heard it ring.

Why Your Dialer Probably Isn't Telling You

Most dialers are designed to track what happens inside their system. They record dials, connections, talk time, dispositions. They report on what they see.

What they don't see is what happens between your system and the carrier. That handoff — where your call leaves your dialer and enters the public voice network — is a blind spot for most contact center operations.

A 487 happens in that gap. The call left your system successfully. Everything looked normal. But it was killed in transit before it could ring.

If you're running a high-volume outbound operation and you've never looked at your 487 rate, you don't know how many dials are being wasted before they reach a single consumer. I've seen operations where 20–30% of attempts were dying at the carrier layer. That's not a call center problem. That's a voice network problem.

What's Actually Killing the Calls

The most common cause today is carrier-layer number flagging. Analytics engines — Hiya, First Orion, TNS — evaluate your numbers in real time as calls traverse the network. If a number has been flagged as Spam Likely or blocked by a carrier, the network may terminate the call before it rings. The 487 is the signal that tells you it happened.

STIR/SHAKEN attestation failures can also contribute. Calls that can't be attested at the A-level face higher termination rates at downstream carriers, particularly with the major wireless networks.

Volume patterns matter too. Numbers that dial at extremely high frequency over short windows trigger carrier-side heuristics that accelerate flagging. Once flagged, 487 rates climb. Most operations don't connect those dots until the contact rates have already deteriorated significantly.

What Your Operation Should Do About It

First, get visibility. If your current voice infrastructure doesn't surface 487 rates per number or per carrier, you're flying blind on a meaningful portion of your outbound traffic. This is not something your dialer vendor can solve — it requires carrier-layer instrumentation.

Second, separate the signal from the noise. Not every 487 is a reputation problem. A spike in 487s on a specific carrier on a specific number pool is a data point worth investigating. A uniform low-level 487 rate across all traffic may be normal. The pattern tells you where to focus.

Third, don't rotate numbers blindly. A common response to declining contact rates is to cycle in fresh numbers. That works, temporarily. But if you're not addressing why numbers are getting flagged in the first place — call patterns, volume velocity, STIR/SHAKEN posture — you'll burn through a new pool just as fast.

The 487 rate isn't a curiosity metric. It's one of the most actionable signals in outbound voice. If you're not tracking it, you're not operating with full information on what your voice network is actually doing.

The Bottom Line

Your dialer tells you what happened inside the system. The 487 rate tells you what happened to the carrier network before a human ever picked up. Those are two different things, and most operations only measure one of them.

If you want to know where your answer rates are really going, start with the signal your dialer isn't showing you.