If you get the below issue , when trying to add a number , this is a ** Microsoft Outage ** 

Set-CsPhoneNumberAssignment -Identity “XXXXXXXXXXXX” -PhoneNumber “612XXXXXXXXXXX” -PhoneNumberType DirectRouting 

Microsoft.Teams.ConfigAPI.Cmdlets.internal\Set-CsPhoneNumberAssignment : LocalizationKey 'Assignment.ErrorResultCode.Mas.RequiredAssignedPlanMissing' was not found
At C:\Program Files\WindowsPowerShell\Modules\MicrosoftTeams\4.3.0\net472\custom\PsExt\Merged_custom_PsExt.ps1:5858 char:9
+ Microsoft.Teams.ConfigAPI.Cmdlets.internal\Set-CsPhoneNumberA ...
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo : InvalidOperation: ({ Identity = ro...iceEnabled = }:<>f__AnonymousType89`5) [Set-CsPhoneNumberAssignment_Set], Exception
+ FullyQualifiedErrorId : InvalidLocale,Microsoft.Teams.ConfigAPI.Cmdlets.Generated.Cmdlets.SetCsPhoneNumberAssignment_Set