It’s not quite walkie-talkie level awesome, and it requires that the person initiating the audio be recognized, know the name of the Google Home speaker the other person is at, and the person at the other end answer, but it’s a start for a decent home intercom.
It doesn’t appear the option is there by default. You’ll need to delete the speaker (or entire Home as some suggest,) and re-set it up again and then you should have Duo calling ability between any audio Google Home speaker. I tried Duo on my mini and once I unlinked and relinked the speaker, Duo appeared.
There doesn’t seem to be any way to do this without first unlinking a speaker and relinking it. Fortunately it doesn’t appear you have to unlink the entire home, just each speaker you want to enable destination Google audio on.
Alternately wait a few days and the feature will probably just show up on all your devices.
The command is “Hey Google Duo Audio call Speaker so and so”. They’ll need to answer, so it’s not exactly intercom functionality, but it’s a start.
Still no “hey google, open an intercom to Maggie’s speaker” but it’s getting there.[9to5Google] & [Android Police]