Requirements

• Enabled “User Sync” on Microsoft 365 Integration.
• Users of MS365 must have the “Office phone” number in an E.164 format.
• Domain for Teams FQDN should be registered in Domains of the MS365 tenant. *.onmicrosoft.com is not supported as the FQDN name of the SBC.
• Certificate issued by one of the following root certificate authorities. (Wildcards are not supported).
• One of the following should be assigned to the MS365 users:

• Microsoft 365 E5
• Microsoft 365 Plan + Microsoft Phone System (add-on) or Business Voice (add-on)

Configuration

Step 1: Configure Teams FQDN

1. Log in to your 3CX Management Console and go to  “Settings” > “Microsoft 365 Integration” > “Teams Direct Routing” tab and check “Enable Microsoft Teams Direct Routing”.
2. Specify the Teams FQDN that match the domain email of MS365. Find your domain by accessing the Microsoft 365 admin portal center > Settings > Domains.

(e.g. MS365 Domain: contoso.com, Teams FQDN can be: teams.contoso.com)

Step 2: Upload certificate and key

1. Get the certificate (including all intermediate certificates) and private key from the certificate root authority. Both should be of *.pem file type.
2. Upload them on the respective controls.

Step 3: Configure dial plan and run script

1. Select your country and area code in the cases that apply. The generated script will be adjusted to format the dialed numbers in scenarios like internal, national, international.
2. Click on “Generate Dial Plan” and save the PowerShell file on your system.
3. Start Windows Powershell as Administrator and ensure that execution policy is set to Bypass.
4. Switch to the folder where the script “teams_dial_plan.ps1” is saved and run.
5. You can verify that the configuration is in place and no errors occur by opening the administration portal of Microsoft Teams.

Step 4: Run scripts for users

1. Users selected on “User Sync” that meet the requirements (license, phone number format) will be included in the generated script.
2. Click on “Generate Users Script” and save the PowerShell file on your system.
3. Review the script for any invalid users that might be commented out. Adjust accordingly and repeat the above steps.
4. Start Windows Powershell as Administrator and ensure that execution policy is set to Bypass.
5. Go to the folder where the script “map_users.ps1” is saved and run.

Note: 

• Configured users with 3CX might take up to 24 hours to be fully functional.
• This step should be executed each time new users are created and assigned a license that enables Teams Phone System capabilities.

Reference:

https://www.3cx.com/docs/microsoft-teams-business-voice/