One disadvantage to any callback system is that once you pick up the phone, if on a PSTN line, you are paying for the call. Then you are paying while the destination number is still ringing. Then you find that there is no answer. OK, you may be able to leave a message, however, if you choose to ring off after a certain number of rings it has still cost you money. It costs you each time you try to make contact.
My suggestion is simple. An option to NOT call back to party A, until party B has answered the call, and that the time party B is called for is 'setting' limited. Thus if party B does not answer then a callback to party A does not occur - thus no cost is ensued.
This means that it would be possible to call party B any number of times without incurring cost - just like on a standard PSTN call - no answer - no pay.
Comments please
