Auto Call Back can help you to save money.

On the other hand, many friends and relatives have minute-based plans, which can be rather expensive if they're calling to other operators.

Rationally, it'd be the best if I call someone with a minute-based plan back and don't accept his call. In this scenario, nobody of us pays anything (extra). Obviously, it's a bit of work - you have to discard the call, go to the call history and call back.

Automatic Call Back

Already two semesters ago, two students (Dominik Brandlberger and Daniel Haslinger) developed a solution to this called "Auto Call Back" (why always invent strange names if it can be that simple?). The whole call-back process is automated by the application.

The result after one semester is a prototype and no commercial application - after all, both didn't have any serious Symbian OS development experience before and the whole issue turned out to be not so easy.

Apparently, you can't easily cancel calls that you don't own through the public CTelephony-APIs of S60 3rd Edition-phones - it only seems to work if you accept them first and immediately cancel them. However, this means that the caller already has to pay up to one minute, no matter how short the call was. Therefore, the application now cancels the calls through simulating the red key. The disadvantage here is that the mailbox has to be turned off for rejected calls.

But how does the app know for which contacts to do it? After the first initial experiments with an own database, the best solution turned out to put all those contacts into a special group. This also allows the user to easily manage the call-back contacts through the normal contacts-app of the phone; the call-back app doesn't have to re-invent the wheel.

The prototype is available for free, but of course not yet ready for real-world usage. It lacks many features and is by far not bug-free. Also, you need to sign it yourself through the Open Signed-process from Symbian Signed.

If anyone is clueless what application to develop next, I'd be very interested in getting a finished and polished application that can do exactly what the prototype can do. Or is there already anything around on the web that I didn't find?