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Spectrum Voice connects a SIP application or phone system to a Spectrum iMessage line. The application can place calls from that line and receive calls made to it.
This guide is about live calls. To send an audio recording inside a message, use the voice() content builder.

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What inbound and outbound mean

  • An outbound call starts in your SIP application. Spectrum places the call from your iMessage line to the phone number you dial.
  • An inbound call starts when someone calls your iMessage line. Spectrum sends the call to your SIP application.
You can set up either direction or both.

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How a call connects

A call uses two kinds of network traffic:
  • SIP signaling contains the instructions to start, answer, and end a call. SIP stands for Session Initiation Protocol.
  • TLS creates an encrypted connection for SIP signaling. Use TLS when you want those call instructions protected in transit.
  • TCP can also carry SIP signaling, but without encryption.
  • RTP audio carries the voices you hear during the call. Spectrum currently uses RTP, not its encrypted form, SRTP. This means the audio on the SIP side of the call is not encrypted.

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What is supported

Inbound and outbound calls have separate settings:
  • For outbound calls, your application connects to Spectrum. Use TLS and Spectrum server port 5061. TCP on Spectrum server port 5060 remains available for compatibility, but it does not encrypt SIP signaling.
  • For inbound calls, Spectrum connects to the SIP address you save in the dashboard. A sips: address selects TLS; a sip: address selects TCP. You can choose the port on which your application listens.
Spectrum does not support SIP signaling over UDP.

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Choose a setup path

Inbound and outbound calling are configured separately. Set up one or both, depending on what your application needs.

Outbound calls

Configure SIP credentials and place calls from your iMessage line.

Inbound calls

Register inbound routing in the dashboard and receive calls in your SIP application.

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Quick reference

For outbound calls, configure your SIP application with these values: You can find the project ID and project secret in your project settings in the Spectrum dashboard. Port 5061 is the server port to enter in your SIP application. Your application does not need to use 5061 as its own local or listening port. To keep an existing TCP configuration, use Spectrum server port 5060 instead. TLS is recommended because TCP does not encrypt SIP signaling. For inbound calls, register the inbound route in the dashboard. The dashboard connects the iMessage line to your SIP application.

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Business profile registration

A business profile is not required to place an outbound call. You can start building and testing before it is registered. However, outbound calls from an unregistered business may be flagged. For production traffic, we recommend registering the business profile in the dashboard. Registration is free and usually takes 1–2 business days.
Business profile registration and inbound route registration are different:
  • A business profile is optional and relates to outbound calling.
  • An inbound route is required if you want to receive calls.

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Current integration model

Voice is documented as a provider because it is a communication platform, but it does not yet use a voice.config() SDK provider. Today, your application connects directly through SIP:
  • For outbound calls, connect your application to Spectrum using TLS on server port 5061. TCP on server port 5060 remains available for compatibility.
  • For inbound calls, save a sips: address for TLS or a sip: address for TCP. This setting is independent of the outbound connection.
  • Allow RTP media traffic for call audio. SIP TLS does not encrypt the RTP audio stream.
  • Use the dashboard to manage the project, business profile, line, and inbound route.
  • Do not expect voice calls in app.messages or app.webhook().
Webhook delivery, SDK call control, and voice-only lines are on the roadmap. No release dates are promised yet.