Syncing is controlled for the most part from Itunes, correspondingly any iphone app would need a complementary pc-based application to communicate with, that had access to the music library, photos, calendar DB, etcetera.
SSH (and more recently SSHFS) are great for certain items - but the photo/music libraries are not readily available to copy over and add items to your iphone's built in libraries. I'm tired of cables, basically, and I don't want to buy any more.
If you have a plan or at least a vague idea of where to start I'd be willing to pitch in and help on this project. I've been looking for a reason to get into cocoa development for a while now, and this is something I'd really like to have as well.