Update Remove-CsOnlineTelephoneNumber.md

Author: JensTrier

skype/skype-ps/skype/Remove-CsOnlineTelephoneNumber.md

@@ -136,6 +136,7 @@ None
 None
 
 ## NOTES
+If one or more of the telephone numbers are assigned to a user or a service, the cmdlet will display an error message and none of the telephone numbers specified will be removed from your tenant.
 
 ## RELATED LINKS
 - [Get-CsOnlineTelephoneNumber](Get-CsOnlineTelephoneNumber.md)