Being able to work with external people of your organization, would be possible thanks to an update that Microsoft is being working recently.
As many of you probably know, when you are using a team in Microsoft Teams, commonly not only involve people from inside the organization, also projects includes people from other organizations, where they have to struggle to be able to catch day to day notifications and files inside those Teams.
Currently, the only method to be able to stay up to date to all the work in different organizations it was to use third party plugins or even to have multiple windows of Teams, being a nightmare to cope with that.
Thus, reduces the productivity of the employees, but also increment problems of security, not only in terms of sign-ins also in terms of information shared…
For those reasons, Microsoft has been working in two updates related with Mirosoft Teams Connect and the access capacities of AzureAD to facilitate the collaboration between orgs.
The first feature includes shared channels which allows that people and teams of different organizations could work in the same Mirosoft Teams without changing the app or event the org where the you are set, which under my point of view is simply fantastic
This feature will be release at the beginning of the next year, but if you’re working under Microsoft org with other Micorosoft Teams, you will be able to see in which direction are taking these new updates.

In my case, the screenshot is from the Microsoft corp teamd organization, but no only shows the Microsoft teams from the Microsot tenant, it also shows one of the teams from the company where I work (showing labelled as external), because I’m connected with my work account.
Also the users would be able to program a meeting in a shared channel, use other applications of Microsoft, and of course, shared the channel with up to 50 teams and external orgs.
From the IT perspective, as always it can be controlled and shut down, in order to configure the “trust relationship” between tenants, and differentiate the collaboration between orgs.
This new features have been highy demanded in the last few months, and probably it will allow Microsoft Teams to be a key tool to communicate internally and externally without problem.