Wendyceja2008, thank you for your inquiry! Great question!
With usage controls, when the controlled line tries to send a text message to a number that has been blocked, they will see a red X in the sent folder and status failed. They will also receive a text message alert “You cannot send messages to destinations that are blocked by the account owner. "
When they try to call a number that has been blocked, the call won't go through. Also a text message alert is received saying, "Your call cannot be completed as dialed. The phone number you are attempting to call has been blocked by the account owner."