Alphabetic JumpList contact names

gistfile1.xml

    <phone:LongListSelector 
        ItemsSource="{Binding}"
        IsGroupingEnabled="True"
        HideEmptyGroups="True"
        LayoutMode="List"
        toolkit:TiltEffect.IsTiltEnabled="True">
        <phone:LongListSelector.ItemTemplate>
            <DataTemplate>
                <Grid>
                    <StackPanel Orientation="Horizontal" VerticalAlignment="Center">
                        <Grid Background="#333" Margin="12,0,0,12">
                            <Image Source="{Binding Contact, Converter={StaticResource Picture}}"
                                    Width="62" Height="62" Stretch="Fill" />
                        </Grid>
                        <TextBlock Text="{Binding Name}" VerticalAlignment="Center"
                                    Style="{StaticResource PhoneTextLargeStyle}"
                                    FontSize="37.333" Margin="18,-19,12,0"/>
                    </StackPanel>
                </Grid>
            </DataTemplate>
        </phone:LongListSelector.ItemTemplate>
        <phone:LongListSelector.JumpListStyle>
            <Style TargetType="phone:LongListSelector">
                <Setter Property="GridCellSize"  Value="111,111"/>
                <Setter Property="LayoutMode" Value="Grid" />
                <Setter Property="Margin" Value="24,19,0,0" />
                <Setter Property="Padding" Value="0" />
                <Setter Property="Width" Value="480" />
                <Setter Property="ItemTemplate">
                    <Setter.Value>
                        <DataTemplate>
                            <Border Background="{Binding Converter={StaticResource BackgroundConverter}}"
                                    Width="111" Height="111" Margin="0,0,12,12" >
                                <TextBlock Text="{Binding Key}"
                                            FontFamily="{StaticResource PhoneFontFamilySemiBold}"
                                            FontSize="48" Padding="6,0,6,12" Margin="6,31,0,0"
                                            Foreground="White"
                                            VerticalAlignment="Center"/>
                            </Border>
                        </DataTemplate>
                    </Setter.Value>
                </Setter>
            </Style>
        </phone:LongListSelector.JumpListStyle>
        <phone:LongListSelector.GroupHeaderTemplate>
            <DataTemplate>
                <Border Background="Transparent" Padding="12,0,0,12">
                    <Border Background="{StaticResource PhoneAccentBrush}"
                            BorderBrush="{StaticResource PhoneAccentBrush}"
                            BorderThickness="1" Width="62" Height="62"
                            Margin="0,0,18,0" HorizontalAlignment="Left">
                        <TextBlock Text="{Binding Key}" 
                                    Foreground="{StaticResource PhoneForegroundBrush}"
                                    FontSize="48" Padding="6" Margin="0,-5,0,0"
                                    FontFamily="{StaticResource PhoneFontFamilySemiLight}"
                                    HorizontalAlignment="Left" VerticalAlignment="Center"/>
                    </Border>
                </Border>
            </DataTemplate>
        </phone:LongListSelector.GroupHeaderTemplate>
    </phone:LongListSelector>