Turning MIT institute phones into pranks

A lot of old and/or broken institute phones show up on reuse these days. Even ifyou aren't from MIT but from any place that uses standardized phones, chances are you might be able to get a hold of extras, discarded ones, etc. What to does one do with them?

Phone that rings by itself
By taking out all the phone's electronics and replacing the solenoid striker (which runs on a high voltage) with a simple 5V motor with a metal object superglued to it, and some simple microcontroller circuitry, it's possible to make a nice prank phone that rings on its own using batteries, with complete disregard to the phone line. This operates on 4 AA batteries that are inside the phone itself, a PIC16F630 microcontroller, and Microchip TC4421's to drive the motor back and forth to strike the bells. It is timed to ring like a phone 30 seconds after it is turned on (with a secret switch on the bottom) and stop ringing when it's picked up. However, when the handset is put down again, it waits another 30 seconds and rings again. What do you do with this? Swap it out for someone's dorm room phone when they aren't watching, and turn it on. When it rings after the preset time, they'll come and pick up, hear nothing, and put it back down. After 30 seconds it'll ring again and repeat until the person is annoyed enough that they (typically) unplug the phone connection for a while - then, watch their surprise when they find out that this phone will yet again ring 30 seconds later, even after it's unplugged! This is especially surprising since these simple, basic phones normally draw their power from the phone line and don't normally have batteries. See a video of the phone ringing by itself, answered, and then turned off via a secret switch on the bottom.

In the works

Modify the above phone to deliver sales calls, etc. (when unplugged)
Phone that squirts water out of the earpiece when answered
Phone that shoots silly string
Phone that has recessed hidden wheels that can allow it to drive off
Phone with built-in cellphone guts that actually works (so people think you're crazy when you're actually talking on a landline phone on a grass field, but it's in fact working as a phone without being plugged)