I have connected a IBM Voice Agent (https://console.bluemix.net/docs/services/voice-agent/getting-started.html) with a Watson Assistant and a Twilio number.
I am able to call my Twilio number and follow a conversation with the assistant.
Now however, I don't want the user to call the number, but rather I want to programmatically trigger the call. Call some API to force the assistant to call some number. Ideally passing some context with it...
I know that Voice Agent uses Voice Gateway behind the scenes (https://www.ibm.com/support/knowledgecenter/en/SS4U29/welcome_voicegateway.html).
Update:
I was able to trigger a call by via Twilio. I ask Twilio to act as an intermediate. Twilio will call both my number and the SIP (Voice Agent) and bridge the call. However I am unable to pass any initial parameters to Watson Assistant since I don't control the process...
As mentioned above, IBM Voice Agent with Watson now allows end users to configure a custom header to extract from inbound SIP INVITE messages. Go to the "Advanced" section under "Edit Voice Agent" to configure it.