code: public void servletInitialized(SipServletContextEvent ce) {
  		ServletContext servletContext = ce.getServletContext();
  		SipFactory sipFactory = (SipFactory) servletContext.getAttribute(SIP_FACTORY);
  		String userName = servletContext.getInitParameter("user.name");
  		String domainName = servletContext.getInitParameter("domain.name");		
  		
  		SipApplicationSession sipApplicationSession = sipFactory.createApplicationSession();
  		// for REGISTER the from and the to headers are one and the same
  		SipURI fromToURI = sipFactory.createSipURI(userName, domainName);				
  		SipServletRequest sipServletRequest = 
  			sipFactory.createRequest(sipApplicationSession, "REGISTER", fromToURI, fromToURI);
  		sipServletRequest.setHeader("Expires", "3600");		
  		sipServletRequest.setHeader("User-Agent", "MobicentsSipServlets");
  		SipURI requestURI = sipFactory.createSipURI(null, domainName);
  		try {
  			Parameterable parameterable = sipServletRequest.getParameterableHeader("Contact");
  			parameterable.setParameter("expires", "0");
  		} catch (ServletParseException e1) {
  			logger.error("Impossible to set the expires on the contact header",e1);
  		}
  		try {			
  			sipServletRequest.setRequestURI(requestURI);				
  			sipServletRequest.send();
  		} catch (IOException e) {
  			logger.error("An unexpected exception occured while sending the REGISTER request",e);
  		}
  	}
docs: /*
  (non-Javadoc)
  @see javax.servlet.sip.SipServletListener#servletInitialized(javax.servlet.sip.SipServletContextEvent)