function FormatPhoneNumber(objPhoneField)
{
   strPhoneNumber = objPhoneField.value;

   strPhoneNumber = strPhoneNumber.replace(/[^0-9]/g, '');

   strAreaCode = strPhoneNumber.substr(0, 3);
   strPrefix = strPhoneNumber.substr(3, 3);
   strNumber = strPhoneNumber.substr(6, 4);

   strFormattedPhoneNumber = strPhoneNumber;

   if (strPrefix.length > 0)
      strFormattedPhoneNumber = "(" + strAreaCode  + ")" + strPrefix
   if (strNumber.length > 0)
      strFormattedPhoneNumber = strFormattedPhoneNumber + "-" + strNumber

   objPhoneField.value = strFormattedPhoneNumber;
}