[ServiceContract]
    public interface IService
    {
        [OperationContract]
        [WebGet]
        DateTime ServerTime(); 
    }

     public class Service : IService
    {
        public DateTime ServerTime() { return DateTime.Now; }
    }

        public string GET(string uri)
        {
            //Web访问对象
            string serviceUrl = string.Format("{0}/{1}", this.BaseUri, uri);
            HttpWebRequest myRequest = (HttpWebRequest)WebRequest.Create(serviceUrl);

            // 获得接口返回值
            HttpWebResponse myResponse = (HttpWebResponse)myRequest.GetResponse();
            StreamReader reader = new StreamReader(myResponse.GetResponseStream(), Encoding.UTF8);

            string ReturnXml = reader.ReadToEnd();

            reader.Close();
            myResponse.Close();

            return ReturnXml;
        }

<?xml version="1.0"?>
<dateTime xmlns="http://schemas.microsoft.com/2003/10/Serialization/">2012-10-15T18:07:44.8028236+08:00</dateTime>