It's a mess regarding the "free" version
"Teams has plenty of frustrations, but it also plays a key role in pulling together the parts of Microsoft's sprawling Office 365 platform in a manner that users can adopt. Teams also fits well with Microsoft's collaboration hardware, from Surface Hub to the newly announced Surface Neo and Duo."
Read like an advert that bit.
So you want to invite someone who's not in an organisation and not in a business. Use the free version. It states it for people not in a business, free lancers don't always have a business account.
You tell them to download Teams from Play on their mobile. They do, they try to sign in with their hotmail account. It claims "Sign-in error. It looks like you aren't a member of any organisation in Teams. Have someone invite you to use the app, or set up Teams for your org. If you've just created a new organisation, try clicking the link in your e-mail." But it's supposed to be a fucking free version, just give me the fucking option to sign in as a guest!
So you choose "Set up teams". Takes you out of the fucking app to the website to sign in. You do, then that pages tells you to download the app from the Play store. And there we have it. Stuck in a never ending fucking loop. As despite claiming there is now a "free" version. Trying to get someone who's not in Office 365 signed in as just a fucking guest, is impossible.
Choosing "Sign up for free" makes no fucking difference.
If they want it to take over, they need to sort that out. As at the moment we only use it internally and use Webex for conference calls.