Using PHP sessions with my android application to login

I am trying to make a login script for my android application, the script will send my email and password to the PHP server, verify the login and then create a PHP session so that the user stays logged in. This is my code,

HttpPost httppost = new HttpPost("http://server.com/login.php");
// Create a new HttpClient and Post Header
HttpClient httpclient = new DefaultHttpClient();

public String login() {

    String userID = "";

    try {
        // Add your data
        List<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>(2);
        nameValuePairs.add(new BasicNameValuePair("email", "e@e.com"));
        nameValuePairs.add(new BasicNameValuePair("password", "admin"));
        httppost.setEntity(new UrlEncodedFormEntity(nameValuePairs));

        // Execute HTTP Post Request
        HttpResponse response = httpclient.execute(httppost);

        userID = EntityUtils.toString(response.getEntity());
        //Log.v("Login response", "" + userID);



    } catch (ClientProtocolException e) {
        // TODO Auto-generated catch block
    } catch (IOException e) {
        // TODO Auto-generated catch block
    }

    return userID;
} 

This script successfully sends data to my server and my PHP successfully logs the user on. I have placed "HttpClient httpclient = new DefaultHttpClient();" outside my main login method. This has helped store the session until I call upon another class, then it just resets the session again. So I am wondering how I can alter the code so that "httpclient" is somehow stored so I can keep the session and stay logged into my server. Thank you!