As far as I am concerned, sonic damage would be force damage, but if you are looking for sonic specifically, one of our members here put together a class that uses sonic damage. Sonamancer, can't remember who put it together exactly but I'll link it.
Edit:
http://www.finalfantasyd20.com/ffd20/sho...hp?tid=306
The Frozen Moogle put it together.
Edit:
http://www.finalfantasyd20.com/ffd20/sho...hp?tid=306
The Frozen Moogle put it together.