function FormatNumber(num, format, shortformat)
{
 if(format==null)
 {
     format = "###-###-#### ";   // Telephone w/ Area Code

 }

 if(shortformat==null)
 {
    var shortformat = "";
 }

 var validchars = "0123456789";
 var tempstring = "";
 var returnstring = "";
 var extension = "";
 var tempstringpointer = 0;
 var returnstringpointer = 0;
 count = 0;

 // Get the length so we can go through and remove all non-numeric characters
 var length = num.value.length;


 // We are only concerned with the format of the phone number - extensions can be left alone.
 if (length > format.length)
 {
  length = format.length;
 };


 // scroll through what the user has typed
 for (var x=0; x<length; x++)
 {
  if (validchars.indexOf(num.value.charAt(x))!=-1)
  {
     tempstring = tempstring + num.value.charAt(x);
  };
 };

 // We should now have just the #'s - extract the extension if needed
 if (num.value.length > format.length)
 {
  length = format.length;
  extension = num.value.substr(format.length, (num.value.length-format.length));
 };

 // if we have fewer characters than our short format, we'll default to the short version.
 for (x=0; x<shortformat.length;x++)
 {
  if (shortformat.substr(x, 1)=="#")
  {
   count++;
  };
 }
 if (tempstring.length <= count)
 {
  format = shortformat;
 };


 //Loop through the format string and insert the numbers where we find a # sign
 for (x=0; x<format.length;x++)
 {
  if (tempstringpointer <= tempstring.length)
  {
   if (format.substr(x, 1)=="#")
   {
    returnstring = returnstring + tempstring.substr(tempstringpointer, 1);
    tempstringpointer++;
   }else{
    returnstring = returnstring + format.substr(x, 1);
   }
  }

 }

 // We have gone through the entire format, let's add the extension back on.
  returnstring = returnstring + extension;

 //we're done - let's return our value to the field.
 num.value = returnstring;
}