As stated in the last update, the ability to use multiple Teams accounts at the same time is being implemented in stages for Desktop. Faster tenant switching functionality on the Windows client has been rolled out to the public ring fully, and Mac will begin rolling out soon. Work is in progress on cross-tenant notification improvements, and support for multiple accounts on desktop will follow. We’ll keep you posted!
Note: The ability to use multiple Teams accounts at the same time is supported on iOS & Android today.
Alex & the Teams team
EditedStephen Dalby commented
Currently I log out of one Tenant and log into the second tenant. However, when a tenant has a separate login security page set up I was unable to log out of that tenant. This has been fixed with the latest update. If being able to change tenants was as simple as it is with Skype for Business, then that would be acceptable. If, however you could have multiple accounts on Teams that would be awesome if you could identify which tenant the team was registered with.
If you are a converted Office 365 user, then it is very likely that you have Live accounts and Family Office 365 tenants. If you are a consultant, then multiple tenant is part of the process and Entrepreneurs also have multiple tenants for each of their start-ups.
Hope this helps