So you have Teams for your own company, and your customer invites you as a guest to his tenant (Article – Expand your collaboration with guest access in Microsoft Teams). Or you are a vendor and work for multiple customers with different tenants accounts. So you want to use multiple Teams accounts at the same time.

Franz 5
At this moment (03 2018), Microsoft Teams Windows Client does not provide an easy way to switch between Teams within multiple office 365 tenants. You can be, but you are not notified each time you have a message, so it makes it useless.
You might workaround by using the windows app for one Team and Chrome for an other Team but you might never check Chrome Teams messages…
I have found a handy way to workaround that, and the solution was in front of me every day but I did not see it !
SOLUTION : Set up Franz to use multiple Teams account
I use the Window app Franz to chat in the same window on whatsapp / facebook messenger / tweeter (multiple accounts) etc.

Window App
Franz has a lot of handy connection to most popular chat tools

Most popular chat tools
And guess what ? There is one for teams too

Microsoft Teams
Add as many Teams service as you have of office 365 tenant, allowing to run multiple instance of Teams within the same Franz Window !
Connect to your tenant, select the guest tenant.
You’ll get notified whenever you have a message in you windows bar

Run multiple instance of Teams within the same Franz Window
Wrap up
You can now chat in multiple tenant Teams and you don’t need the Windows Team appanymore!! The downside are notifications, less informative than the Teams windows app but that’s a workaround… waiting for Microsoft to release this feature.
Reference:
Angama, J (2018). How to connect to multiple tenants in Microsoft Teams ! The user friendly guide. Available at: https://jeffangama.wordpress.com/2018/03/23/how-to-connect-to-multiple-tenants-microsoft-teams-the-user-friendly-guide/ (Accessed: 23 April 2018)