How to trace private calls on cell phone?

ok today I recieved a call on my cell from a private number. When I answered it all the girl did was scream then hung up? I dont think its a help thing more like a prank. How can I find out what the number is? Its on att/cingular and im in states

Contact the provider of your cell phone service.

go 2 the police station they are the only 1s that can trace those calls,trust me they have traced me before!!!

can people trace private/restricted numbers by looking at their phone bill and all the call logs? cause I found out my parents can look at who I call. =O but if I prank call someone can they trace it back to my number?

every morning at 6am I get a private call, they dont say anything but I can hear the tv in background. what can I do to stop this? it is causing problems in my marriage!

I can go to any of my local authorities b/c the problem involves them and I have contacted my provider but they can't do anything but change my number and I have already had it changed 3 times. These private calls are not only calling me but all 5 of my mother's phones which include a nearly 80 year old. I have a different provider and I live in another state. These calls come at all times night day and they always say some extremly ignorant things. I have bought a recoreder and plan on recording them and keeping a log. But who can I get to trace these private numbers on my 6 cell phone numbers. They have also hacked into a few of our accounts on the internet. My family is at aloss on what to do. My father even tried getting lawyers but no one will take on the case b/c they all are associated with our local authorities. (city police, county, state and FBI)