I\'m running Zynergy on a 5600 now, and love it.
Yes, it uses the Sharp PIM apps. I don\'t think you can replace them without rebuilding the ROM, but you can install somthing else. I\'ve added KO/PI to mine for a datebook. It\'s great, and I even have it syncing with my laptop via wireless/SSH. I\'m using Korganizer on the desktop, but evolution should also work. I haven\'t tried anything else for the address book; I don\'t need to sync it, just keep a backup every so often.
I haven\'t run into many apps that won\'t run. If they don\'t it\'s usually because they depend on some odd or old library, not anything to do with sharp/zynergy incompatibilities.