Matrix user forums

I have made a burgler alarm to my house and I want
to let it call me on my old mobil phone when something
is wrong.

My old mobil phone is still working, but how can I
let my code dial the number of my new mobil phone ?

Some phones may allow you to send AT commands via some kind of serial communication (wired or virtual via Bluetooth). Otherwise, you might need to write an application of the phone.