/**
* get a magento shipping method identifer for either:
* - the shipping method used by $address
* - the first of all valid shipping methods
*
* @param Mage_Customer_Model_Address_Abstract
* @return string
*/
public function getUsableMethod(Mage_Customer_Model_Address_Abstract $address)
{
$this->fetchAvailableShippingMethods();
return $address->getShippingMethod() ?: $this->getFirstAvailable();
}