Hi!
I am afraid there is no specific trail version of Teams for your phone system.
If you want to deploy Direct Routing in Microsoft Teams, please make sure you meet the following infrastructure requirements for the supported SBCs, domains and so on.
https://learn.microsoft.com/en-us/microsoftteams/direct-routing-plan#infrastructure-requirements
Then you can configure Microsoft Phone System and enable users to use Direct Routing by following these steps:
Step 1. Connect the SBC with Microsoft Phone System and validate the connection
Step 2. Enable users for Direct Routing, voice, and voicemail
Step 3. Configure voice routing
Step 4. Translate numbers to an alternate format
For more details about it, you can refer to:
https://learn.microsoft.com/en-us/microsoftteams/direct-routing-configure
If the response is helpful, please click "Accept Answer" and upvote it.