WPF

namespace WindowsPhoneTestApp
{
   public partial class TestControl : UserControl
   {
      public static readonly DependencyProperty nameProperty = DependencyProperty.Register(
            "name",
            typeof(string),
            typeof(TestControl),
            new PropertyMetadata("99999"));

      public string name
      {
         get { return (string)GetValue(TestControl.nameProperty); }
         set { SetValue(TestControl.nameProperty, value); }
      }

      public TestControl()
      {
         InitializeComponent();
         DataContext = this;
      }
   }
}

<UserControl x:Class="WindowsPhoneTestApp.TestControl"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    xmlns:local="clr-namespace:WindowsPhoneTestApp"
    mc:Ignorable="d"
    FontFamily="{StaticResource PhoneFontFamilyNormal}"
    FontSize="{StaticResource PhoneFontSizeNormal}"
    Foreground="{StaticResource PhoneForegroundBrush}"
    d:DesignHeight="92" d:DesignWidth="328">
    
    <Grid x:Name="LayoutRoot" Background="{StaticResource PhoneChromeBrush}" Height="88" Width="324">
        <StackPanel>
            <TextBlock Name="text" Text="{Binding name, Mode=OneWay}" FontSize="48" Foreground="#ffffffff" Height="88" />
        </StackPanel>
    </Grid>
</UserControl>

public class DataSource : INotifyPropertyChanged
   {
      public DataSource()
      {
      }

      private string _dataName = "default name";
      public string dataName
      {
         get { return _dataName; }
         set
         {
            if (_dataName == value)
            {
               return;
            }
            _dataName = value;
            this.NotifyPropertyChanged("dataName");
         }
      }

      #region INotifyPropertyChanged
      public event PropertyChangedEventHandler PropertyChanged;

      private void NotifyPropertyChanged(String info)
      {
         if (PropertyChanged != null)
         {
            PropertyChanged(this, new PropertyChangedEventArgs(info));
         }
      }
      #endregion
   }

<code>
public DataSource dataSource { get; set; }

      // Constructor
      public MainPage()
      {
         InitializeComponent();
         dataSource = new DataSource();



         DataContext = this;
         
         dataSource.dataName = "new name";
      }
</code>

<code>
<!--ContentPanel - place additional content here-->
        <Grid x:Name="ContentPanel" Grid.Row="1" Margin="12,0,12,0">
            <TextBlock Text="{Binding dataSource.dataName}" Style="{StaticResource PhoneTextNormalStyle}"/>
            <local:TestControl name="{Binding dataSource.dataName}"/>  
        </Grid>
</code>