Why Can’t I Make or Receive VoIP Calls?

You’ve moved your business to a VoIP system for a reason—flexibility, scalability, and cost savings. But when calls suddenly stop working—either incoming, outgoing, or both—it can bring operations to a standstill.

Whether you’re supporting a growing team or handling all IT duties solo, this post will walk you through five of the most common reasons you may be having issues with VoIP calls, and what you can do to fix them—fast.

1. Check Your Internet Connection First

VoIP (Voice over IP) relies entirely on your internet connection. Before diving into device settings or configurations, take 30 seconds to confirm:

1. Is your internet working at all?
2. Can other devices browse the web or stream?
3. Are other cloud-based tools (email, CRM) functioning?

If the connection is down across the board, reboot your modem and router. Still no dice? You may need to contact your ISP—or better yet, consider a provider like Fusion Connect that offers built-in failover and SD-WAN options to keep your voice services running even during outages.

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2. Restart Your Router, Switches, or Phones

“Did you try turning it off and then on again?” Yes, it’s cliché—but power cycling your equipment often works.

• Unplug your router, any network switches, and VoIP phones or DECT base stations (like the Grandstream DP752)
• Wait 30 seconds
• Plug in your router and wait for it to fully boot before powering up other hardware

This resets your device’s connection to the network and often resolves temporary glitches caused by congestion, outdated IP leases, or traffic misrouting.

Pro Tip: For multi-line setups, check if all phones are affected or just one. A device-specific issue may point to a configuration error or faulty cable.

3. Verify SIP Registration and Account Info

If your phone shows “Not Registered” or “SIP Registration Failed,” it likely means it’s not connected to your VoIP provider.

What to check:

• Username and SIP password entered correctly?
• SIP server address matches your provider’s (e.g., sip.fusionconnect.com)?
• Firewall blocking SIP ports (typically UDP 5060)?
• Device or softphone configured to use correct transport (UDP/TCP/TLS)?

Fusion Connect customers using Grandstream, Poly, or Yealink handsets can reference our device configuration guides for exact steps.

4. Inspect Cables, Headsets, and Power

It might seem obvious, but don't skip the physical stuff:

• Is your Ethernet cable securely plugged in?
• Is the PoE (Power over Ethernet) port working?
• For DECT phones, is the base station powered and within range?

Faulty headsets or speakerphones can also cause one-way audio issues, so test calls using the handset or speaker to isolate the problem.

5. Double-Check Softphone or App Settings

If you're using a softphone app, here’s what to look for:

• Is your device connected to Wi-Fi or cellular data?
• Is Do Not Disturb (DND) mode enabled?
• Have your login credentials recently changed?
• Is your app set to auto-register at startup?

For mobile or remote teams, a VPN or SD-WAN solution can improve call quality and ensure your VoIP traffic is prioritized over less critical data.

Still Stuck? Let’s Talk.

If you’ve walked through these steps and still can’t make or receive calls, it’s time to escalate. Let’s Connect

Fusion Connect customers benefit from 100% U.S.-based support, advanced monitoring tools, and proactive alerts to catch problems before they impact business.

We’re happy to help you diagnose the issue—and if your current provider isn’t pulling their weight, we’re ready when you are.