Details of the pitch control
The way pitch is controlled in the Habitat Intercom device is fairly simple. I replaced the pitch resistor in the toy with a photo sensitive resistor, that i put in a black plastic tube in front of the controlling computers monitor. The amount of light reaching the photo resistor is controlled by varying the color (grey scale actually) of a square area right in front of the tube, or by sliding the photo resistor back and forth in the tube. This system gives a reasonable degree of control, and "repeatability" over the playback pitch.

The inspiration for this system came from Ghazalas Video Octavox device that has pitch controlled by 8 photo resistors mounted with suction cups on a TV screen.

Here's a picture of the setup with the photo resistor in the tube in front of the sequencer program i wrote.

The colour of the little black / grey / white squares in the bottom of the picture are copied to the square in front of the tube during playback.
MikMo.dk > Circuit Bending > Schematics > Computer interface > Pitch control