Teams cannot chat with Skype Users

connorhatcher Hello, this is still in preview so I suppose that's one reason for the official docs being inconsistent and incomplete. I think I have to raise a GitHub on the Docs for this.

They mention that you can toggle it on using Teams admin center

Manage external access (federation) - Microsoft Teams | Microsoft Docs

But I've never actually heard of anyone succeeding in doing that so that's why we use PowerShell as also mentioned here 

Manage external access (federation) - Microsoft Teams | Microsoft Docs 

But that's not all steps required and the others are instead listed here

Teams and Skype interoperability - Microsoft Teams | Microsoft Docs

So you would have to verify these settings (1, 2, 3) and also be aware of the online vs hybrid scenario Manage external access (federation) - Microsoft Teams | Microsoft Docs

1. Set-CsExternalAccessPolicy
-EnablePublicCloudAccess

"Indicates whether the user is allowed to communicate with people who have SIP accounts with a public Internet connectivity provider such as MSN. The default value is False."

2. Set-CsTenantFederationConfiguration
-AllowPublicUsers

"When set to True (the default value) users will be potentially allowed to communicate with users who have accounts on public IM and presence providers such as Windows Live, Yahoo, and AOL. The collection of public providers that users can actually communicate with is managed by using the Set-CsTenantPublicProvider cmdlet."

3. Set-CsTenantPublicProvider
-Provider

"Indicates the public provider (or providers) that users will be allowed to communicate with. Valid values are:"

• AOL
• WindowsLive
• Yahoo

Let me know how it goes!