Bring 2 separate offices together for better omnipresent collaboration through a virtual window is the main use case of the free app Perch.
Users can dedicate an iPhone or iPad as a portal to link to another location running the same app to create an always-on video conference.
The app uses face detection to enable audio, every time you want to talk to the other office, just look into that iOS device. Otherwise, it mutes the audio but the video is always on.
The video below explains how the app works.