They'll tell you on the phone. You DO NOT want to go to the Bell County Jail. That place is insane. I won't even drive through Bell County. No joke. I got arrested for a simple speeding ticket I had forgot about. I was arraigned with 2 other guys. One was in for an over due library book and the other for not having a headlight on his bicycle. I heard the judge read the charges, so i KNOW it was true. The jailers are total *******'s.
The only way to find out if you have a warrant in a specific area is to visit the area police and ask the police at the front desk to search their records. However, if they do find that you have a warrant they may arrest you at that very moment. For details, check http://www.ehow.com/how_5414531_out-warrants.html.