I figured part from the box just opening when you enter the correct code I also wanted some sound. To keep the vintage feel it needed to be a bell of some sort. I had some solenoids and bells from old phones lying around end tried the out.

Since I didn't want to bother with an H-bridge for the phone assembly seen below I combined a loose bell I had with a solenoid that actuates from DC pulses (polarity agnostic) and then springs back. This little contraption (now mounted on a board) also ensures that I get only one singe "bing" wich is what I want. Now I can drive this with one or two channels from the steppers darlington array (I'll have some channels/transistors to spare).

The ringing keeps going for a good while!