If you are serious about iPhone communication then check out the iRule application for home remote control. You'll need to install X10 or a similar option w. IP control hardware onto your garage door (and connect it to your router). Basically you're looking for an IP controlled low voltage relay switch. Be careful when you punch a hole in your firewall so you can control the door remotely; you don't want someone to hack it and gain access to your home. Total cost if you do your own work is going to be over $100. Alternatively, get the $30 keypad and call it a day.

edit: there may be a bluetooth controlled relay option available which would eliminate the IP issues but you'd have to be within 25 feet, wait for bluetooth pairing, and then hit the open/close button.