I have a real basic question...when installing a new service release, do the ring tones on the phones, certain models or all models, get reset to the default?
Addition of SR does not affect the configurations. So your answer NO, it wont reset your ringtones.
What about firmware upgrades to the phones?
I believe two ringtones (chirp 1/2) are actually built into the phone firmware, so these could change although it's unlikely.
The ringlist.xml and associated tones that you add could be overwritten by upgrades in theory, so you'd be wise to have them backed up...
All the ring tones are still there, just the users' settings were not retained after the upgrade.
For example, if I had my default ring set to vibe, after the upgrade my ring tones were reset to default.