I would not superglue the buttons that is a little extreme and irreversible(the following week the customer may get complaints from the teachers that one could easedrop on the classroom or they want the option to have their classroom to ring takes about 15 mins per phone to do what I suggest.) you can open the phones and put black tape over the switch circuit below the auto ans button and enable it with another phone like the fella above suggests.I have done this on the 123211D phones and and Delta Galaxy phones were the customer wanted something crazy or system was just not as flexible as they are now.....and the had to reverse it later when they realized How messed up their request was !!