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?