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Inbound calling sends calls received by your Spectrum iMessage line to your SIP application. You must register inbound routing in the dashboard. Configuring outbound SIP credentials does not create the inbound route automatically.

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Before you start

You need:
  • A Spectrum project.
  • An iMessage line in that project.
  • A SIP application or phone system that can receive calls over TLS or TCP.
  • A public hostname or IP address that Spectrum can reach.
  • Firewall access (network permission) for the SIP listening port and the RTP audio ports used by your application.
WhatsApp numbers cannot be used for Spectrum Voice.
If the SIP application runs on a private network, such as a laptop on home or office Wi-Fi, it is not normally reachable from Spectrum. Configure port forwarding and firewall rules, or run the application on a public server.

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Set up inbound calling

1

Open the project

Sign in to the Spectrum dashboard and select the project that owns the iMessage line.
2

Open inbound voice registration

Open the project’s inbound voice registration and choose the iMessage line that should receive calls.Make sure you select an iMessage line. WhatsApp numbers are not supported.
3

Register the inbound route

In the SIP URI field, enter the address that Spectrum should call. Use sips: for encrypted TLS signaling or sip: for unencrypted TCP signaling:
Replace agent with the SIP username or extension expected by your application, and replace voice.example.com with its public hostname. The final number is the port on which your application listens. A port tells Spectrum which network service to contact on that server.If the application does not require a specific username or extension, omit agent@. For example:
Port 5061 is the default for sips: and 5060 is the default for sip:. These are defaults, not requirements. To use a different listening port, include that port in the URI. UDP is not supported.The dashboard also has optional Username and Password fields. Fill in both fields only if your SIP application requires username-and-password authentication for incoming calls. This standard SIP mechanism is called SIP Digest. Otherwise, leave both fields empty.
4

Configure your SIP application

Configure the application to listen using the same transport and port as the SIP URI saved in the dashboard.For TLS, the application needs a TLS certificate and its private key. For production, use a publicly trusted certificate that is valid for the hostname or IP address in the SIP URI. TCP does not require a TLS certificate.
5

Keep the SIP application available

Start the SIP application and make sure Spectrum can reach its public hostname or IP address and SIP port.Also allow the application’s RTP port range through the firewall. RTP carries the call audio and normally uses UDP; check the application’s media or RTP settings for its exact port range.
6

Place an inbound test call

From another phone, call the iMessage line registered in the dashboard. Confirm that your SIP application receives the call and that audio works in both directions.

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What each registration does

The word “registration” can refer to two different settings: Registering a business profile does not create an inbound route. Registering an inbound route does not register the business profile.

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Before going live

  • The inbound route is saved under the correct project.
  • The selected number is an iMessage line, not a WhatsApp number.
  • The SIP application uses the routing values shown in the dashboard.
  • The saved SIP URI uses sips: for TLS or sip: for TCP.
  • The application listens on the transport and port specified by the saved SIP URI.
  • The TLS certificate is valid for the hostname or IP address in the SIP URI when using TLS.
  • Spectrum can reach the application’s public hostname or IP address and SIP port.
  • A test call reaches the application and has working two-way audio.
  • The firewall allows the application’s UDP RTP port range. SIP TLS does not encrypt the RTP audio stream.

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Troubleshooting

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No inbound call arrives

Check that the inbound route is saved for the exact iMessage line being called. Then confirm that the SIP application is running, publicly reachable, and listening on the transport and port specified by the saved SIP URI. If the application runs behind a router or cloud firewall, confirm that traffic on the SIP port is forwarded to the application.

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The wrong project or line receives the call

Open the inbound registration in the dashboard and verify both the selected project and iMessage line. The inbound route is tied to that selection.

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The SIP application tries UDP

Select TLS or TCP explicitly in the SIP application. Spectrum Voice does not accept SIP over UDP.

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A TLS route does not connect

Confirm that the route starts with sips:, the receiving application listens for TLS on the configured port, and its certificate covers the hostname or IP address in the route. Also confirm that the firewall allows inbound TCP traffic on that port.

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The call arrives but audio does not work

SIP TLS protects signaling only. Audio uses RTP, so confirm that the endpoint’s firewall allows the UDP RTP port range configured in the SIP application. If the application is behind a router, its NAT or port-forwarding configuration must also send that traffic to the application. NAT is the router feature that lets devices on a private network share a public internet address.

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I configured outbound calls, but inbound does not work

Outbound credentials and inbound routing are separate. Return to the dashboard and register the inbound route for the iMessage line.