A simple, but very important feature, is inserting a ringback tone to the caller even if the destination number is not yet ringing. Most of the lost calls come from silence where the destination ringback tone takes too long and the caller hangs up thinking the call will did not go through.
The ringback overlay also insures that the payphone recognizes the ringback tone and thus, returns the money when there is no answer. Many times there are such a variety of ringback tones that the payphone will not recognize ringing and collect the money.
Call completion rates shot up from around 35% to 60% as soon as the ringback overlay was implemented; a monumental breakthrough.
