preferably a 2.5 mm phone jack

Two applications:

Should be useable as shutter release trigger for still image capture compatible to DSLR remote trigger devices.
(http://www.doc-diy.net/photo/eos_wired_remote/). In this "trigger mode" the Beta would capture an image and write a raw file to µSD card once triggered.

Should be useable as continuous external video clock trigger. Where every pulse received on the trigger port is forwarded to the sensor and starts reading one video frame.