If my laptop ever gets stolen, I want it to make an attempt to "phone home" so that I can track it down.
What can I set up to accomplish this?
Prey is an open source program that does exactly what you want (it also happens to run all major operating systems, including Ubuntu of course).
Prey lets you keep track of your phone or laptop at all times, and will help you find it if it ever gets lost or stolen. It's lightweight, open source software, and free for anyone to use. And it just works.
Note: Prey also offers some commerical services, but you are not required to buy anything to use the software.