[ServiceContract]
    public interface ICustomerService
    {
        [OperationContract]
        List<Customer> GetCustomers();

        [OperationContract]
        bool SaveCustomers(Dictionary<Customer, string> Customers);
    }

[AspNetCompatibilityRequirements(RequirementsMode = AspNetCompatibilityRequirementsMode.Allowed)]
    public class CustomerService : ICustomerService
    {
        #region ICustomerService Members

        public List<Customer> GetCustomers()
        {
            using (var DB = new NorthwindDataContext())
            {
                var query = from c in DB.Customers
                            select c;
                return query.ToList();
            }
        }

        public bool SaveCustomers(Dictionary<Customer, string> Customers)
        {
            TODO: Implement Save
            return true;
        }

        #endregion
    }

public class CustomerDataSource
    {        
        public CustomerDataSource()
        {
            LoadCustomers();
        }

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

            };
            client.GetCustomersAsync();
        }

        ObservableCollection<Customer> _Customers = new ObservableCollection<Customer>();
        public ObservableCollection<Customer> Customers
        {
            get {
                return _Customers;
            }

        }     
    }

<UserControl xmlns:data="clr-namespace:System.Windows.Controls;assembly=System.Windows.Controls.Data"  x:Class="SilverlightConsumeWCF.MainPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="clr-namespace:SilverlightConsumeWCF">
    <UserControl.Resources>
        <local:CustomerDataSource x:Key="Customers" />
    </UserControl.Resources>    
    <Grid x:Name="LayoutRoot" Background="White">
        <data:DataGrid ItemsSource="{Binding Path=Customers, Source={StaticResource Customers}}">
        </data:DataGrid>
    </Grid>
</UserControl>