Yes, there's actually an iPhone app for opening and closing your garage door. It's much easier to beam that signal from your phone, though the Internet, and through a home network than just pointing a dedicated garage door opener in the general direction of your garage.
The folks at mydooropener.com have developed a do-it-yourself iPhone garage door opener kit. The process involves buying some electronic parts and installing them on your garage door opening unit. Then simply download the software onto your computer and iPhone and you're all set. There are both hard-wired and WiFi versions, with nearly identical pricing.
Altogether the parts for the setup will set you back no more than $100. The instructions are fairly straightforward and there's a step-by-step guide. Carefully look at the directions before taking the plunge. Though it seems simple enough, this project may not be for beginners.
All communication from the phone and home unit is encrypted with passwords that change for every use. One of the only issues to be concerned with is accidentally opening the garage door when away and not knowing it's open. Luckily there's an easy way to check the status of your garage door with the app.