Infinite scrolling or LongListSelector

lls.xaml

<phone:LongListSelector Name="ItemList"
  ItemsSource="{Binding Items}"
  ItemRealized="ItemList_ItemRealized"> <!-- this is the important listener for the scrolling -->
  <!-- your items -->
</phone:LongListSelector>

lls.xaml.cs

// the offset knob defines after how many "fresh" loaded items (which get visible while scrolling) 
// the list should load new items
private int _offsetKnob = 2;

// this is the current page number
public int PageNumber { get; set; }


public YourListControl()
{
  // set page number to first page 
  PageNumber = 0;
  InitializeComponent();
}


// this listener listens to the event, which is triggered when new items are realized.
// While scrolling new items are shown in the viewport -> so they are realized
// just play with the offsetKnob property to get the correct behavior
private async void ItemList_ItemRealized(object sender, Microsoft.Phone.Controls.ItemRealizationEventArgs e)
{
  // in case the items are not null
  // and the items are more than the offset knob
  // and they are actual items (could be a list footer too)
  if (ItemList.ItemsSource != null && ItemList.ItemsSource.Count >= _offsetKnob && e.ItemKind == LongListSelectorItemKind.Item)
  {
    // check if you hit the last item, after which you want to trigger the loading of new items
    // that's where you need the offsetKnob
    if ((e.Container.Content as Item).Equals(ItemList.ItemsSource[ItemList.ItemsSource.Count - _offsetKnob]))
    {
      // load new items and increment PageNumber afterwards
      await (DataContext as MainViewModel).UpdateLists(++PageNumber);
    }
  }
}

MainViewModel.cs

// your items
public ObservableCollection<Item> Items { get; set; }

// your items per page
private int _bufferSize = 15;


// populate the Items member
public async Task UpdateLists(int page = 0)
{
  ObservableCollection<Item> items = await GetAllItems(); // or however you want to get your items
  
  // skip page * bufferSize items and take bufferSize items
  List<Item> newItems = items.Skip(page * _bufferSize).Take(_bufferSize)).ToList();
  
  if (page > 0)
  {
    // append the new items to the end of the list
    newItems.ForEach(item =>
    {
      Items.Add(item);
    });
  }
  else
  {
    // replace all items in case it is the first page
    Items = newItems; 
  }
}