I don't think that approach would be very practical. Most users won't have access to cron.
I think a better alternative might be a wap enabled, php driven, web page or to use the actual MMS protocol. mMode equiped phones can also select an image and, with one click, upload it to an image server. The wap or HTML pages would allow the user to actually log in and select category links instead of requiring the user to memorize category numbers.
In any case, I think development time required for this mod is too much to take on at this time and it's not of critical importance for me. If anyone else wants to persue this, I wish them all the best.