I recently was in a similar situation as them, I didn’t dive very far into it at the time but it pretty much boiled down to Rhythmbox requiring GVFS/Gnome Virtual File System for iPhone/iPod detection. I don’t think it supports the KDE equivalent of GVFS (kio-fuse I think?), at least in regard to detecting iPod/iPhone.
@4L3X I wasn’t able to get it to work either, but hopefully this helps point in the right direction to find the solution!