title: How to override magento function?
body: <p>I have added prefix and telephone field on customer registration page and want to use that value in checkout billing address</p>
  
  <p>So , I have to override magento \app\code\core\Mage\Checkout\Block\Onepage\Billing.php for customer selected prefix and telephone.</p>
  
  <p>I want your help to override this particular functions in local</p>
  
  <p>public function getPrefix() { ... }</p>
  
  <p>Please help me ... </p>