Here's the first half of the magic, kids.
These Belkin Wifi outlets are great. They can be controlled from your phone, from anywhere. They cost about $50 at Apple, Target, etc. A bit steep for turning a light on, but I found it a justifiable cost for this use. Certainly there are many other ways to do this same thing (Raspberry Pi, Arduino, laptop, unused cellphone), but this was easy and took about a half hour once I had the supplies in hand.
Setup is really easy. The Wemo connects itself to your home Wifi router and becomes accessible from your phone via their app.
The coolest part is that IFTTT (If This Then That) now supports the Wemo! If you're not familiar with this, then I'll tell you about that .(see what I did there?)
.It's a free service which connects many different data sources together based on simple rules called recipes. It can even control certain hardware, like this Belkin switch or the Philips LED Hue light bulbs.
More on IFTTT later.