function CallMe(src,dest)
 {     
     var ctrl = document.getElementById(src);
     // call server side method
     if (ctrl.value.length >= 4) {
         PageMethods.GetContactName(ctrl.value, CallSuccess, CallFailed, dest);
     }
 }

 // set the destination textbox value with the ContactName
 function CallSuccess(res, destCtrl)
 {     
     var dest = document.getElementById(destCtrl);
     dest.value = res;
 }

 // alert message on some failure
 function CallFailed(res, destCtrl)
 {
    // alert(res.get_message());
 }