Microsoft has decided, as a policy, that they do NOT want to allow any 3rd party audio integration for Teams. They want to force customers to procure audio conferencing from Microsoft only. They are only allowing 3rd party audio conference integration with Teams for Government clients only at this time.
Our management is pushing Microsoft hard to change this decision/policy on behalf of our 6,000+ business customers. Thus far, this is what they have decided as a policy. You can visit the Microsoft User Voice page to “Vote” for MSFT to allow 3rd party audio integration with Teams as well as post comments and express your opinions https://microsoftteams.uservoice.com/forums/555103-public/suggestions/32070235-support-3rd-party-audio-conferencing-provider-acp.
This has a link to the Teams LinkedIn group https://www.linkedin.com/groups/3411197/