mutex <keyname> [on|off]

<extension name="mutex_example">                                                                                                                            
      <condition field="destination_number" expression="^5000$">                                                                                                
        <action application="set" data="mutex_feedback=$${us-ring}"/>                                                                                           
        <action application="set" data="execute_on_post_originate=mutex $destination_number off "/>                                                             
        <action application="mutex" data="$destination_number on"/>                                                                                             
        <action application="bridge" data="group/$destination_number"/>                                                                                         
      </condition>                                                                                                                                              
    </extension>