[DocOrtho]

I have flat rates and don't use real time calculations. It was just as easy to edit the shipping/shipping.php file:

Around line 288

  if   (!$enable_shipping ||   $config["Shipping"]["realtime_shipping"] !=   "Y") {
      #
      # Get ALL shipping methods   according to the conditions (W/O real time)
      #
      $shipping = func_query("SELECT   * FROM $sql_tbl[shipping] WHERE active='Y' $destination_condition   $weight_condition ORDER BY orderby"); 

Change to:

if (!$enable_shipping || $config["Shipping"]["realtime_shipping"] != "Y") {
  #
  # Get ALL shipping methods according to the conditions (W/O real time)
  #
  // {{{ func_is_postal_box()
/**
 * This function checks to see if the customer's
 * shipping address is a United States Post Office
 * Box.
 *
 * @param string $address Customer's Street Address
 * @return boolean true if post office box; false if not
 */
function func_is_postal_box($address) {
  $postalBoxRegex = '/^([pP]{1}(.*?)[oO]{1}(.*?))?([bB][oO]?[xX])(\s+)([0-9]+)/iD';

  @preg_match($postalBoxRegex, trim($address), $isPostalBox);

  if (is_array($isPostalBox) && (count($isPostalBox) > 0)) {
    return true;
  }
  else {
    return false;
  }
}
// }}}  
  if (func_is_postal_box($userinfo['s_address'])){
  $shipping = func_query("SELECT * FROM $sql_tbl[shipping] WHERE active='Y' AND code='USPS' $destination_condition $weight_condition ORDER BY orderby");
  }else{
   $shipping = func_query("SELECT * FROM $sql_tbl[shipping] WHERE active='Y' $destination_condition $weight_condition ORDER BY orderby");
  }