Sounds like a complicated project. What kind of DVR do you have, and what kind of phone do you have? There are easier ways of doing it, if you don't mind running a second app to handle the garage door portion of it. For example, My Door Opener for iPhone uses an Arduino-based system:
http://mydooropener.com/
The Arduino system receives signals via the built-in Ethernet port, and then hands them off to a relay board. The iPhone app sends the signal to control door open/door close. And since it's all pre-made, the bulk of the work is already done for you. Tutorial here:
http://mydooropener.com/downloads/My...ructions-2.pdf