Venky, dumb question, but any idea if the call control can occur during a live call (two endpoints are connected instead of just one endpoint connected to plivo

Venky, dumb question, but any idea if the call control can occur during a live call (two endpoints are connected instead of just one endpoint connected to plivo)? I'm trying to write an app that depends on this functionality but can't seem to do it in twilio or tropo. Also, does plivo provide a softphone or client library?