How to insert data to Mobile Services - Windows Phone (Windows Azure)

using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Navigation;
using Microsoft.Phone.Controls;
using Microsoft.Phone.Shell;
using myPhoneApp.Resources;

using Microsoft.WindowsAzure.MobileServices;
using Newtonsoft.Json;

namespace myPhoneApp
{

    public class MyMember
    {
        public int Id { get; set; }

        [JsonProperty(PropertyName = "username")]
        public string Username { get; set; }

        [JsonProperty(PropertyName = "password")]
        public string Password { get; set; }

        [JsonProperty(PropertyName = "name")]
        public string Name { get; set; }

        [JsonProperty(PropertyName = "tel")]
        public string Tel { get; set; }

        [JsonProperty(PropertyName = "email")]
        public string Email { get; set; }

    }

    public partial class MainPage : PhoneApplicationPage
    {

        private MobileServiceCollection<MyMember, MyMember> items;
        private IMobileServiceTable<MyMember> memberTable = App.MobileService.GetTable<MyMember>();

        // Constructor
        public MainPage()
        {
            InitializeComponent();
        }

        private async void btnSave_Click(object sender, RoutedEventArgs e)
        {
            try
            {
                items = await memberTable.ToCollectionAsync();
                var insertItem = new MyMember { Username = txtUsername.Text
                    , Password = txtPassword.Password
                    , Name = txtName.Text
                    , Email = txtEmail.Text
                    , Tel = txtTel.Text
                };
                await memberTable.InsertAsync(insertItem);
                items.Add(insertItem);
                MessageBox.Show("Register Data Successfully.");
            }
            catch (MobileServiceInvalidOperationException ex)
            {
                MessageBox.Show("Error : " + ex.Message);
            }
        }
    }

}