Shortly you can add anyone as guest in Microsoft Teams!!
Yes you heard it right. As we’re starting to roll out, shortly you will see the ability to add anyone with a business or consumer email account, such as Outlook.com, Gmail.com or others, can participate as a guest in Teams with full access to team chats, meetings and files. As you aware previously, anyone with an Azure Active Directory (Azure AD) account could be added as a guest, and now anyone with an email address can be added to a team. All guests in Teams are covered by the same compliance and auditing protection as the rest of Office 365, and can be managed securely within Azure AD.
Also read, Guest Access in Microsoft Teams.