You may already have heard about Kaizala (https://products.office.com/en/business/microsoft-kaizala), a simple chat solution for work – allowing communication between people inside and outside of your organization directory using mobile phone and phone number-based identity.
This has been first released to selected marker (mainly India).
Now, it is becoming an integrated member of the Office 365 family (not yet there) and will be integrated with Microsoft Teams within the next 12 to 18 months.
You can start using Kaizala by accessing the Kaizala administration portal (https://manage.kaiza.la/)
If you have not yet been using it, you will need to enable it for your organization by accessing the Settings option.
You can skip the phone registration step
From there you can manage the registered phone numbers, compliance settings and application permissions
From there you are good to go and start using Kaizala
NOTE until the Kaizala Pro license becomes available in Office 365, all your user will have to sign in using with phone number. Once available, all licensed users will be able to sign-in with the corporate/work account
They can also start without installing any app on their mobile by accessing the web based interface https://webapp.kaiza.la/, but you will have to import their phone number first
You can also create Kaizala groups based on Office 365 Groups or Distribution Lists