Methods to handle premium rate subscriptions. <p>Stops a subscription to the supplied mobile number from the calling account.</p><b>Parameters</b> <table border="1" width="500"> <tr valign=top> <td width="100">mobilenumber</TD> <td>The mobile number of the subscriber.</td></tr> </tr> </table><br>Returns the contact ID for the contact related to the subscription. If the subscription relates to a non-contact for the account, an empty Guid is returned. Methods to handle premium rate subscriptions.