Cell Phones - how can a phone call trigger a system?

Hi
I'd like to use a cell phone to trigger the start of an electrical event in my system.

Is there a circuit board type component for phone calls, or must I connect a pay per call inexpensive  phone from Best Buy?
Can the ring tone generate an electric signal / sound in the 1/8 inch sound port, to initiate the other elements? When cells are rung, do they automatically send signal to the sound output?

Thanks