Save on longdistance calls by an alert

Just wondering if its possible to make an app to run with the clock once you make a call, and alerts/beep a few seconds (10) every minute during a call. Or perhaps to stablish manually when to beep. For example, to warn you 10 seconds before you reach a 2, 3 or 10 minute call, so you hang up before reaching the desire minutes.

This could be very helpfull when making long distance calls, and of course save some buks. Of course in places that carges per minute.