Legitimate process servers do not call to warn you, or to get money from you to stop the process. They will deliver the notification without warning.
(Here is more info than you really need on process serving:
http://en.wikipedia.org/wiki/Service_of_proce ... nited_States.29 )
Also, if you were threatened with an "arrest warrant" via a phone call or email, read this:
http://news.uscourts.gov/warning-arrest-warrant-scam
"The warrant is phony. A valid warrant would not be served by fax or e-mail. It would be served in person by a U.S. Marshal or other law enforcement officer."
"Anyone receiving a fake arrest warrant should contact the FBI or the district U.S. Marshals Office. If there is any question regarding the authenticity of a warrant, contact your district clerk of court."