The Fremantle daemon that decodes ringtones seems to have a bug that, in some cases, makes it produce wave files with an invalid size in them. These files cannot be played by libcanberra, so it meant that some ringtones couldn’t be played when you receive a phone call. I just released ringtoned 0.2.1 with a work around for the bug, please let me know if this version works better for you.
Anyway, I got a new component in the Meamo Bugzilla for ringtoned, so please report bugs there.
Update 2: I released ringtoned 0.2.2 that just adds some more debugging info to make my life easier.