private static SforceService Login()
{
   // this is the web reference object generated by Visual Studio
   SforceService service = new SforceService();
 
   // Need to append password and security token together since we're logging in through the 
   // Salesforce API
   string passwordPlusSecurityToken = string.Format("{0}{1}","password","token");
 
   LoginResult loginResult;
   try
   {
      loginResult = service.login("salesforceUsername", passwordPlusSecurityToken);
   }
   catch (SoapException ex)
   {
      // Log error
      return null;
   }
 
   /** 
     * Once the client application has logged in successfully, it will use
     * the results of the login call to reset the endpoint of the service
     * to the virtual server instance that is servicing your organization
   */
   service.Url = loginResult.serverUrl;
 
   /** 
   * The client application now has an instance of the SforceService
   * that is pointing to the correct endpoint. Next, the sample client
   * application sets a persistent SOAP header (to be included on all
   * subsequent calls that are made with SforceService) that contains the
   * valid sessionId for our login credentials. To do this, the 
   * client application creates a new SessionHeader object and persists it to
   * the SforceService. Add the session ID returned from the login to the
   * session header.
   */
   service.SessionHeaderValue = new SessionHeader();
   service.SessionHeaderValue.sessionId = loginResult.sessionId;
 
   return service;
}