Video Doorbell With IQ 4

How do video doorbells integrate with ADC and IQ4? Which doorbell or camera do I buy? Are there extra monthy charges I will be charged for?

Alarm.com compatible cameras connect to your local network, typically via Wi-Fi, to integrate with your Alarm.com account directly. Some cameras can be viewed from the Qolsys Panel once connected to the ADC account.

You can live view/answer the Alarm.com comaptible Skybell or the Alarm.com VDB 770 from the IQ Panel 4. Steps on how to integrate this found in the below guide:

Video service requires an additional monthly service charge. If using one Video Doorbell Camera, the Video Doorbell Only add-on can be enabled. Service plan changes are made directly through your Surety account via System Manager.

Compatble Doorbell cameras include:

ADC-VDB770.
ADC-VDB101/2 Alarm.com SkyBell HD
ADC-VDB105/6, ADC-VDB105x/6x, Alarm.com Skybell Slim

A list of cameras and specs can be found in the below guide

I have a nutone intercom system with the doorbell speaker at front door. I wonder if the transformer for the door chime puts out the correct voltage? Can you tell me voltage requirements?

Intercoms are not compatible, voltage varies from camera to camera. See the below installation guides for reference:

Is there a way to use my existing 2gig doorbell to trigger (ADC rules) a camera with 2 way audio, and the video will show up on panel and phones so I can keep my existing doorbell setup this would be the most aesthetic option for my setup.

Live view from the panel is a live stream that access, and Event Triggered clip would not generate at the panel. You must request the live stream manually.