If the guest does not have a camera or microphone, it is still possible to have a successful conversation, this article describes the steps the guest can take to enter the conversation without a camera, microphone or speakers.
The guest doesn't have a camera:
If the guest doesn't have a camera they can simply choose to enter the meeting with 'no camera' to successfully enter the meeting.
The guest doesn't have a microphone or speakers:
If the guest doesn't have a microphone or speakers they can simply enter the meeting without microphone or speakers. Once in the meeting they can dial-in to establish an audio connection
Tip: If the guest doesn't have any speakers they can simply plug-in any earphones they might have.