Before you contemplate configuring Services and Users, you should review whether your Network, Firewall and Router settings are prepared to handing Teams SIP VOIP calls.
This Microsoft article will assist with this:
Preparing Your Network For Microsoft Teams
We do not recommend locking down firewalls to specific IP addresses for your VOIP Portal traffic. Our IP Addresses can and will change as required as the service expands. However you can check the existing addresses and modify your Firewall settings if required.