@lcuk Dbus message is emitted and it contains the phone number, which is enough to look for the contact. I'm not familiar with flite, have been using espeak to test this. No idea about the contacts database being able to store custom ringtones. It would also need a way to override the original completely.
I am all for it though, if someone can help to override the ringtone!

@Matan: I haven't tried with mplayer, only with espeak and alwayson. Maybe I should try with mplayer too since with espeak just saying a name can go pretty fast and is not ideal for troubleshooting the issue. Thanks.