Dictionary<Customer, string> _ChangedObjects = new Dictionary<Customer, string>();
        public void RegisterChangeTracking(Customer c)
        {
            c.PropertyChanged += (sender, e) => 
                { 
                    var cus = sender as Customer;
                    if (_ChangedObjects.ContainsKey(cus))
                        _ChangedObjects[cus] += ";" + e.PropertyName;
                    else
                        _ChangedObjects.Add(cus, e.PropertyName);
                };
        }

private void LoadCustomers()
        {
            CustomerServiceClient client = new CustomerServiceClient();
            client.GetCustomersCompleted += (sender, e) =>
            {
                foreach (var c in e.Result)
                {
                    _Customers.Add(c);
                    RegisterChangeTracking(c);
                }

            };
            client.GetCustomersAsync();
        }

private void SaveCustomers()
        {
            CustomerServiceClient client = new CustomerServiceClient();
            client.SaveCustomersCompleted += (sender, e) =>
            {
                var b = e.Result;
            };
            client.SaveCustomersAsync(_ChangedObjects);
        }

private CustomerDataSource CustomerDataSource
        {
            get
            {
                return this.Resources["Customers"] as CustomerDataSource;
            }
        }

        private void ButtonSave_Click(object sender, RoutedEventArgs e)
        {
            CustomerDataSource.Save();
        }

public bool SaveCustomers(Dictionary<Customer, string> Customers)
        {
            using (var DB = new NorthwindDataContext())
            {
                var query = from c in DB.Customers
                            where Customers.Keys.Select(cus => cus.CustomerID).Contains(c.CustomerID)
                            select c;

                var lst = query.ToList();
                Type t = typeof(Customer);
                foreach (var kv in Customers)
                {
                    var oldCustomer = kv.Key;
                    var newCustomer = lst.Single(cus => cus.CustomerID == oldCustomer.CustomerID);

                    foreach (var s in kv.Value.Split(new char[] {';'}, StringSplitOptions.RemoveEmptyEntries))
                    {
                        var propInfo = t.GetProperty(s);
                        var v = propInfo.GetValue(oldCustomer, null);
                        propInfo.SetValue(newCustomer, v,null);
                    }
                }

                DB.SubmitChanges();
            }
            return true;
        }