code: public String getCallId() {
  
  		CallIdHeader id = (CallIdHeader) this.message
  				.getHeader(getCorrectHeaderName(CallIdHeader.NAME));
  		if (id != null){
  			if(logger.isDebugEnabled()) {
  				logger.debug("getCallId - return=" + id.getCallId());
  			}
  			return id.getCallId();
  		} else {
  			if(logger.isDebugEnabled()) {
  				logger.debug("getCallId - returning null");
  			}
  			return null;
  		}
  	}
docs: /*
  (non-Javadoc)
  @see javax.servlet.sip.SipServletMessage#getCallId()