Of course it is possible, with automaitized(not human tasks).

The #{seamComponent.customAction('Initial')} will invoke this method of the Seam component.
In this method you can make any external(voip/webservice) or internal invocation.
And you have an option the define timer too.

     <task-node name="taskNameXYZ">
          <event type="node-enter">
               <action expression="#{seamComponent.customAction('Initial')}"></action>
          </event>
          <transition to="transisionToxyz"></transition>
     </task-node>