Isn’t brilliant that by using a disposable cell phone you can trigger fireworks? Basically it has two soldered wires to the phone and attaching them to a hobby fuse which ignites when current is passed through it.

He has wired into the speaker leads for the speaker phone. When the phone rings, the current sets off a thyristor allowing for a battery pack to be discharged into a rocket fuse. These fuses heat up and ignite, and use them to light fireworks fuses pretty easily.

The next idea was to have it recognize dial tones and set individual fuses off, but that would require a microcontroller and a much more complex hack.