using System;

using System.Linq;

using System.Xml;

using System.Xml.Linq;

public class Program

{

    public static void Main()

    {

        var xDoc = XDocument.Parse(xmlString);

        // with Descendents

        var status = xDoc.Descendants("optinStatus").Single();

        Console.WriteLine(status.Value);

        // with Element

        var customer = xDoc.Root.Element("customer");

        var optinStatus = customer.Element("optinStatus");

        Console.WriteLine(optinStatus.Value);

        // for attribute

        var response = xDoc.Descendants("response").Single();

        var attr = response.Attribute("status");

        Console.WriteLine(attr.Value);

    }

    private static string xmlString = @"

<response op=""getcustomerinfo"" status=""200"" message=""ok"" version=""1.0"">

  <customer>

    <totalMsg>3</totalMsg>

    <custId>9008281</custId>

    <custName></custName>

    <timestamp>2015-04-30 16:17:19</timestamp>

    <optinStatus>3</optinStatus>

    <custMobile>6185312349</custMobile>

    <subacct>1st Choice Courier</subacct>

  </customer>

</response> 

    ";

}