It does seem like you are locked into the ring tone under User Preferences. Like an OBi ATA there is an X_DefaultRing on each SP trunk. There should be a way to override the User Preference with the trunk setting, but I can't find it. Blanking out the ring tone didn't work. The User Guide was zero help.
FYI setting Alert-Info to bellcore-dr4 works on an OBI ATA.