Getting the following error message when trying to remove a dial-plan from Exchange Server 2010, we are moving to Exchange 2016 and want to remove all Dial-Plans from our remaining Exchange 2010 UM servers.
The UM server can't be added to the DialPlanName UM dial plan. The UM dial plan has more UM languages available than the UM server does.
See that it uses the Set-UMServer cmdlet and basically re-sets the server with the remaining dial-plans. These UM servers have the necessary language packs needed for the remaining dial-plans.
We would remove all dial-plans but we take the approach of removing one and then see if there are any side effects and then remove the next one, then the next one, etc.