code: public SipPrincipal getUserPrincipal() {
  		if(this.userPrincipal == null) {
  			if(this.getSipSession() != null) {
  				this.userPrincipal = this.getSipSession().getUserPrincipal();
  			}
  		}
  		return this.userPrincipal;
  	}
docs: /*
  (non-Javadoc)
  @see javax.servlet.sip.SipServletMessage#getUserPrincipal()