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
Editedbart kemps commented
Guest access just doesn't work.
(No I do not mean it is impractical. I think it WOULD be impractical. If it worked.)
The Windows Teams Client just logs me in as another user if I switch company.
The Android Client simply crashes, or returns me to the guest company account.