WP8 NavigationService::Navigate only takes an URI as an argument. It will then throw if you try to navigate to a view that has ctor dependencies. Call on line 14 of Welcome.xaml.cs will throw.

Login.xaml.cs

public partial class Login : PhoneApplicationPage
{
  ILoginService _service;
  
  public Login(ILoginService service)
  {
      this.InitializeComponent();
      _service = service;      
  }
  
  //do whatever here that uses ILoginService
}

Welcome.xaml.cs

public partial class Welcome : PhoneApplicationPage
{
    public Welcome()
    {
        this.InitializeComponent();
    }

    private void GetStartedButton_Click(object sender, RoutedEventArgs e)
    {
    }

    private void LoginButton_Click(object sender, RoutedEventArgs e)
    {
        this.NavigationService.Navigate(new Uri("/Views/Login.xaml", UriKind.Relative));
        // This call will throw because Login.xaml doesn't have a parameterless constructor
    }
}