In fact, Google Home's hands-free calling is separate from your smartphone altogether.
While in call, you can place people on hold and ask the Google Assistant info. If, for example, you are living with roommates (Google Assistant can recognize up to six different voices), the device will be able to detect who is asking Google Assistant to call their own dad.
On the upside, the Google Voice and Project Fi can link their numbers to Home to make their number available on the caller ID of recipients. Because Google Home already works with multiple accounts and does voice recognition, it will work correctly for all users. Just head into the Assistant settings within the Google Home app and you can have your phone number displayed to the recipient. The feature allows for voice calls to any U.S. or Canadian number, including landlines or cellphones. It's not entirely clear right now what the user experience will be like when you call a business (but see the video below). You're simply getting earlier access to new features before they're released broadly.
It appears that Google Home will operate as a speaker phone, allowing the conversation to happen totally through the device.
Also of note, calls to 911 are not yet supported. Now, there's no way to call someone else's Google Home; it only supports outgoing calls, and the only way to use feature is with your Google Home device. Amazon basically made its Echo lineup far superior to Google Home in terms of communication functionality, but now, mere moths later, Google is leveling the playing field with a "hands-free calling" feature.
Has hands-free calling started working on your Google Home? Already having been launched in the USA and accessed by some Canadian users, this feature allows up to six different individuals to be recognized based on their voices.
In other words, it does not work like Amazon's Alexa calling feature, which lets you call from one Echo to another Echo and even call someone's Alexa app. As is the case with most Google Home updates, the United States should see it first, followed by Canada shortly after. French language support is coming soon, according to Google.