1. Overview
  2. Troubleshooting & Help
  3. Carrier Rejected & Calling Health - Best Practices (Non-Technical Guide)

Carrier Rejected & Calling Health - Best Practices (Non-Technical Guide)

Why Are My Calls Failing?

If your calls aren’t going through, it's often not because of your platform or internet - it’s because your number is being blocked or rejected either by the person you're calling or their phone company (carrier). The two most common reasons are tied to specific call failure codes:

❌ What Do “603” and “608” Errors Mean?

SIP Code 603 – “Decline”

  • What it means: The person you're calling rejected the call.

  • Why does it happen?

    • They tapped “Decline”.

    • They blocked your number.

    • They use an app that auto-blocks unknown or suspicious calls.

  • What you should do:

    • Don’t keep calling the same people who rejected you.

    • Clean your contact lists - remove inactive or unresponsive numbers.

    • Build better caller trust (see best practices below).

SIP Code 608 – “Rejected by Carrier”

  • What it means: The phone company blocked your call before it rang.

  • Why does it happen?

    • Your number looks like spam to phone networks.

    • You’re calling too fast or too many people at once.

    • Your number has a bad reputation from past calls.

  • What you should do:

    • Register and verify your phone numbers (see below).

    • Don’t overuse a single number - rotate them.

    • Use a trusted phone provider that supports verification.

Best Practices To Improve Call Success

1. ✅ Register Your Numbers

  • Go to FreeCallerRegistry.com

  • Register all your business phone numbers.

  • This tells phone networks you’re a legitimate business, not a scammer.

Why it's important: Carriers and spam filters check this registry before letting your calls go through. If you’re not listed, they may block you automatically.

2. 🛡️ Use Verified Caller ID and Branding

  • Make sure when someone gets your call, they see:

    • Your correct business name

    • A verified caller ID

  • This builds trust and reduces the chance of being flagged as spam.

Pro Tip: Tools like Hiya, First Orion, and Caller ID Reputation can help you monitor how your number is seen by others.

3. 🔁 Use a Number Pool (Rotate Your Numbers)

  • Don’t rely on just one phone number for all your calls.

  • Use a pool of numbers and rotate between them.

  • Spread out your calling activity.

Why it helps: When one number makes too many calls too quickly, it raises red flags. Rotation keeps your activity looking more natural.

4. 🌡️ Warm Up Your Numbers

  • Start with a small number of calls per day.

  • Gradually increase call volume as people answer, engage, and don’t block you.

  • Focus early calls on contacts likely to pick up.

Why?: Just like warming up an email address, this helps build your number's reputation. Starting big too fast makes it look suspicious.

5. 🔍 Check Your Number’s Reputation Regularly

Use services like:

  • CallerAPI.com – budget-friendly spam score checker

  • Hiya, TNS, First Orion – industry-grade analytics

These tools will tell you:

  • Is your number listed as spam?

  • Does it show your caller name correctly?

  • Has it been marked as unwanted by others?

6. 🔐 Use STIR/SHAKEN Authentication (If Available)

  • A modern system that tells phone networks:

    • “This is a real, verified caller.”

  • Reduces the chance of being marked as spam.

Note: This is usually managed by your phone provider. Ask them to give your number the highest verification level (called “A-Level Attestation”).

7. 📋 Follow Legal Rules

  • Respect Do Not Call (DNC) lists.

  • Follow time-of-day rules for calling.

  • Only call people who have given permission when required.

Failing to follow these rules increases complaints—which damages your reputation.

8. 🧼 Keep Your Call Lists Clean

  • Don’t keep calling people who:

    • Already said “No”.

    • Declined your call repeatedly.

    • They are not responding at all.

Why? Repeated call failures (603/608) are tracked. The more you rack up, the more your number gets penalized.

9. 🛠️ Use a Quality Provider That Supports These Features

Look for a phone system that lets you:

  • Import and rotate numbers

  • Manage caller ID and verification

  • Analyze call logs

  • Integrate with third-party reputation checkers

📈 What Do the Metrics in the Number Portal Mean?

Term What It Means
Telephony Status How analytics networks see your number (e.g., Spam, Uncertain)
Verified Whether your number is registered and verified (via FreeCallerRegistry, etc.)
Caller ID What shows up when you call someone (name, business, or "Unknown")

📘 Resources

Was this article helpful?