Your company uses Microsoft Skype for Business Server 2015 and Enterprise Voice as the PSTN solution.

You plan to migrate all users to Microsoft Teams Calling Plans.

You will decommission Skype for Business Server after the migration is complete.

You need to ensure that all the users retain their current phone number once the migration is complete. The solution must minimize the downtime of PSTN features for each user.

What should you do first?

A. From the Microsoft 365 admin center, purchase Communications Credits for all the users.

B. Schedule a port order for the phone numbers of all the users.

C. From the Microsoft Teams admin center, order phone numbers for all the users.

D. Migrate all the users to Teams.

Reference:
https://docs.microsoft.com/en-us/microsoftteams/phone-number-calling-plans/transfer-phone-numbers-to-teams