Hello Stephen Zink,
Thank you for posting in Q&A forum.
If you want to enable support for Microsoft Teams for 10 users in an on-premises Exchange Server 2019 environment and don't currently have a Microsoft 365 license. Without a 365 license, you cannot directly enable Teams for any user because the use of Teams is based on a cloud service and requires a corresponding license to activate.
If you don't have a Microsoft 365 license, to support 10 users using Teams, you need to purchase 10 corresponding Microsoft 365 licenses for those 10 users. Once these users have valid licenses, they can log in to the Microsoft 365 platform and start using Teams.
Also, since you also mentioned on-premises Exchange 2019 Server, you may also need to configure a hybrid authentication and sync service (such as Azure AD Connect) so that while these 10 users are using Teams, their mailboxes still remain on the on-premises Exchange server and achieve a certain level of integration with cloud services such as Outlook on the web.
Recommended reference links: Hybrid deployment prerequisites | Microsoft Learn
Exchange Server hybrid deployments | Microsoft Learn
Configure Microsoft 365 Groups with on-premises Exchange hybrid | Microsoft Learn
I hope the information above is helpful.
Best Regards,
Yanhong Liu
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