Modern garage door openers use frequencies around 315 MHz. It is not possible for your BlackBerry to transmit RF at those frequencies, so an app using the BlackBerry by itself would not be possible. However, it would be possible to create a remote control app that operated using the cell signal. You'd have to dedicate a phone line to receive the calls, and build some hardware to interface the phone line to the garage door opener, but that would be well within the capability of an electronics tinkerer. It might be possible to buy the capability in a commercial package, especially for industrial applications or an X-10 type controller.
