Important Warning For Small Inquisitive Children: Do not begin with an Armatron[1]. You're ready to fiddle with all the wires and figure out a way to remotely operate the way-too-many-degrees-of-freedom controls, only to find that it's all mechanical, there's only a single motor running the whole thing![2], and your parents are probably going to be home before you can pick all the bits of gearbox out of the cat's dinner bowl and try to reassemble them. Claims that those grinding, crunching noises "were always there" are unlikely to pass muster.
As I discovered with a similar system, a cheap arm's motions are also not easily repeatable. I wanted to pick up CDs and move them around via robotic arm, with something similar to the Armatron. We discovered that there's enough slop in the system as to make anything remotely precise impossible.
This is the most annoying mobile scrolling I've ever seen. What could possess anyone to make this? Sorry to be off point, but the scrolling makes it half impossible to read.
Steps include buying pre-made remote-controlled robot-arm from Maplin/OWI (http://www.owirobot.com/products/Robotic-Arm-Edge.html) for $55.99 and connecting it to a computer running Linux (which in this article seems to be free!) REEAAAALL awe-inspiring indeed. (read: linkbait) [EDIT: Just saw that you can also buy a 'USB interface' for it. Ha!]
[1] https://secure.wikimedia.org/wikipedia/en/wiki/Armatron
[2] http://www.starborneworks.com/?p=22