From the FBI...

The phone rings, you pick it up, and the caller identifies himself as an officer of the court. He says you failed to report for jury duty and that a warrant is out for your arrest. You say you never received a notice. To clear it up, the caller says he'll need some information for "verification purposes"-your birth date, social security number, maybe even a credit card number. This is when you should hang up the phone. It's a scam.

Read more at... http://www.fbi.gov/page2/june06/jury_scams060206.htm