For some reason I got it into my brain that interfacing the rotary control with a PIC chip would be a good idea. I can only think of a couple of vague uses for it at the moment and none are particularly useful, but I hope to do something cool with this in the future.
Step 1: Go get stuff.
1 - Rotary phone
3 - 220 ohm resistors
2 - 0.1uF capacitors
2 - 20K resistor (can substitute anything between 10K and 47K)
2 - LEDs
1 - PIC development board (I used the Basic Micro development environment)
1 - 20 MHZ resonator or crystal
1 - Breadboard
1 - 5V power source
1 - A foot or so of hookup wire
1 - Screwdriver
1 - Wire stripper
Step 2: Dissect the phone.
There will be four wires running from the rotary dialer to this junction-box-like thing. The wires should be held in place by little more than tightened screws. Loosen the screws and disconnect the wires.
After that, disconnect the rotary dialer from the phone itself.