var submitcount=0;

function reset() {
document.callbackForm.name.value="";
document.callbackForm.phone.value="";
}

function checkCallback() {                    
if (   	  	  	  	  	  	  	  	  	  	  	  
	(document.callbackForm.name.value=="") ||
	(document.callbackForm.phone.value=="")
	)  
   {
   alert("Please enter your contact name and telephone.");
   return false;
   }

else 
   {
   if (submitcount == 0)
      {
      submitcount++;
      return true;
      }
   else 
      {
      alert("This form has already been submitted.");
      return false;
      }
   }
}