return sessionMap.remove(id);
CallSession session = sessionMap.remove(id);  if(session != null) { Collection<CallSession> sessions = userSessionMap.get(session.getUsername());  sessions.remove(session);   if(sessions.size() == 0) { userSessionMap.remove(session.getUsername()); } } return session;
    public CallSession destroyPhoneSession(String id) {        return sessionMap.remove(id);    }