diff --git a/sms.api.php b/sms.api.php
index 5f4ead7..349fe47 100644
--- a/sms.api.php
+++ b/sms.api.php
@@ -9,13 +9,25 @@
  * Defines information for an SMS Gateway.
  *
  * @return array
+ *   An associative array of gateways where the key is a globally
+ *   unique identifier for the gateway and the value is an associative array
+ *   of gateway attributes with the following keys:
+ *   - "name": The display name of the gateway.
+ *   - "send": The callback for sending the message. See sms_send_log() for an
+ *     example.
+ *   - "configure form": (optional) The callback of the form constructor for
+ *     configuring the gateway.
+ *   - "send form": (optional) The callback of the form constructor for adding
+ *     additional elements to the sms_send_form.
+ *   - "validate number": (optional) A callback for validating a phone number.
+ *   - "format number": (optional) A callback for formatting a phone number
+ *   - Any additional values.
  */
 function hook_gateway_info() {
   return array(
     'my_gateway' => array(
       'name' => 'My Gateway',
       'send' => 'my_gateway_send',
-      'receive' => TRUE,
       'configure form' => 'my_gateway_admin_form',
       'send form' => 'my_gateway_send_form',
     ),