No Azure AD Account Necessary
Today, if you invite someone with a Google account to join an application that supports Azure B2B Collaboration (like Teams, Office 365 Groups, or Planner), that person ends up with a guest user account in your tenant’s Azure Active Directory.
In the future, that guest account won’t be needed because Microsoft is enabling federation for Google accounts. The feature is now in preview and works for accounts with a Gmail.com address. What it means is that Azure AD will recognize the credentials belonging to Gmail.com accounts when their owners try to access applications in your tenant.
Apps Might Still Need Guest User Accounts
It’s early days yet and the documentation is naturally sparse because it focuses on getting federation going with Google and doesn’t get into the details of how this might apply to applications like Teams and Office 365 Groups. My guess is that guest user accounts might still be needed for applications that depend on memberships, but we shall see in time.
For more information on Office 365 Groups, see Chapter 11 in Office 365 for IT Pros. Azure B2B Collaboration and how invitations result in guest user accounts is covered in Chapter 12, while Teams is in Chapter 13 and Planner in Chapter 15.