What are the technical requirements for audio calls?
You can make browser-based audio and video calls via Userlike. You don't need a phone number from the contact and can transition from a chat to a call.
Audio call connections are made through Twilio. See the following links to learn more about the requirements to establish connections:
Which IP ranges and protocols need to be whitelisted for video calls can be seen here: https://www.twilio.com/docs/video/ip-addresses