Passing a values in URL

Hey Guys. I am working on an API for automated voice application.

I was just wondering if it is possible to send a URL value with out assigning anything to it.

For example if someone presses a key on their telephone keypad, the application will go the following url <Gather action=\"confirmation_verificationphp?est_delivery_time\">

The "delivery_time" is not assigned to anything, I just want PHP to preform a set of actions when it gets the "delivery_time"

Below is a clear example

// When user enters a number on their telephone keypad it will go to "confirmation_verification.php?delivery_time"
  echo "<Gather action=\"confirmation_verification.php?delivery_time\" method=\"GET\" timeout=\"10\" finishOnKey=\"*\">";
                    echo say("Please enter your estimated delivery time");
                   echo "</Gather>";


Preform the set of actions when you get "delivery_time"
                   if($_GET['delivery_time']) {
                      $delivery_time =  $_GET['Digits'];
                      send_order_confirmation_email($order_number, $delivery_time );
                   }