The voicemail said:
XXX-XX-XXXX
I'm gonna fuck you up.
Where the Xs represent = my SSN.
You might also want to look into lifelock. I think SSN protection is key, even if you go forward with criminal prosecution fixing that shit is a pain in the ass. It also goes a long way toward substantiating your claim (as a plaintiff) of distress and having to take preventative measures against his threat.
W/r/t what he could be charged with, depending on how ambitious your local police department is: forgery and counterfeiting, identity theft (bad juju in CA), criminal threatening, possibly terroristic threat. This differs from state to state, but here in PA it does not necessarily have to involve physical harm. (Though "I'm gonna fuck you up" could certainly be construed that way).
"A terroristic threat... may mean an offense against property or involving danger to another person that may include but is not limited to recklessly endangering another person, harassment, stalking, ethnic intimidation, intimidation and criminal mischief."
The penalty in California for your particular case probably falls closer to the misdemeanor side of the spectrum (though certainly not so if he actually takes any action torward identity theft).
In CA "the court can impose probation (informal) with or without jail time, community service, physical labor, counseling, restitution (paying the victim), fines ($200 to $2,000), and “stay-away” orders. A conviction also results in the person having a
permanent criminal record."
It would be very difficult for him to obtain future employment with the latter.