Using Local Database for Application

using System.Data.Linq;
using System.Data.Linq.Mapping;

After that you need to define the model by hand.

//Model Class
[Table]
public class EmailClass
{
    [Column(IsDbGenerated = true, IsPrimaryKey = true)]
    public int Id { get; set; }
    [Column()]
    public string EmailAddress { get; set; }
}

Once the model is defined you then need the DataContext

public class EmailContext : DataContext
{
    public EmailContext(string sConnectionString)
        : base(sConnectionString)
    { }

    public Table<EmailClass> Emails
    {
        get
        {
            return this.GetTable<EmailClass>();
        }
    }
}

Connection string would look like,

string ConnectionString = "Data Source=isostore:/EmailDB.sdf";

Some reusable methods to Add and Display

public IList<EmailClass> GetEmails()
{
    List<EmailClass> emails = new List<EmailClass>();
    using (var db = new EmailContext(ConnectionString))
    {
        var query = from e in db.Emails
                    select e;
        emails = query.ToList();
    }

    return emails;
}

public void AddEmail(EmailClass _email)
{
    using (var db = new EmailContext(ConnectionString))
    {
        db.Emails.InsertOnSubmit(_email);
        db.SubmitChanges();
    }
}

Then comes UI which would help you to save and display data,

<Grid x:Name="ContentPanel" Grid.Row="1" Margin="12,0,12,0">
    <Grid.RowDefinitions>
        <RowDefinition Height="Auto"></RowDefinition>
        <RowDefinition Height="*"></RowDefinition>
    </Grid.RowDefinitions>
    <StackPanel Grid.Row="0" Orientation="Horizontal">
        <TextBox Width="300" x:Name="txtEmail"></TextBox>
        <Button HorizontalAlignment="Right" x:Name="btnSave" Content="Save" Width="120" Click="btnSave_Click"></Button>
    </StackPanel>
    <ListBox x:Name="lstEmails" Grid.Row="1" >
        <ListBox.ItemTemplate>
            <DataTemplate>
                <StackPanel>
                    <TextBlock Text="{Binding Path=EmailAddress}"></TextBlock>
                    <TextBlock Text="-----"></TextBlock>
                </StackPanel>
            </DataTemplate>
        </ListBox.ItemTemplate>
    </ListBox>            
</Grid>

The complete code is as below,

using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Animation;
using System.Windows.Shapes;
using Microsoft.Phone.Controls;
using System.Data.Linq;
using System.Data.Linq.Mapping;

namespace WP7_Samples
{    
    public partial class LocalDB_WP7 : PhoneApplicationPage
    {
        const string ConnectionString = "Data Source=isostore:/EmailDB.sdf";
        public LocalDB_WP7()
        {
            InitializeComponent();

            InputScope _scope = new InputScope();
            InputScopeName _scopeName = new InputScopeName();
            _scopeName.NameValue = InputScopeNameValue.EmailNameOrAddress;
            _scope.Names.Add(_scopeName);

            txtEmail.InputScope = _scope;

            using (var db = new EmailContext(ConnectionString))
            {
                if (!db.DatabaseExists())
                    db.CreateDatabase();

                LoadData();
            }
        }

        public void LoadData()
        {
            lstEmails.ItemsSource = GetEmails();
        }

        public IList<EmailClass> GetEmails()
        {
            List<EmailClass> emails = new List<EmailClass>();
            using (var db = new EmailContext(ConnectionString))
            {
                var query = from e in db.Emails
                            select e;
                emails = query.ToList();
            }

            return emails;
        }

        public void AddEmail(EmailClass _email)
        {
            using (var db = new EmailContext(ConnectionString))
            {
                db.Emails.InsertOnSubmit(_email);
                db.SubmitChanges();
            }
        }

        private void btnSave_Click(object sender, RoutedEventArgs e)
        {
            if (txtEmail.Text.Trim() != "")
            {
                var emailObj = new EmailClass() { EmailAddress = txtEmail.Text.Trim() };
                AddEmail(emailObj);
            }
            LoadData();
            txtEmail.Text = "";
        }
    }

    //Model Class
    [Table]
    public class EmailClass
    {
        [Column(IsDbGenerated = true, IsPrimaryKey = true)]
        public int Id { get; set; }
        [Column()]
        public string EmailAddress { get; set; }
    }

    public class EmailContext : DataContext
    {
        public EmailContext(string sConnectionString)
            : base(sConnectionString)
        { }

        public Table<EmailClass> Emails
        {
            get
            {
                return this.GetTable<EmailClass>();
            }
        }
    }
}