// To retrieve:
var offlineContacts = instance.get_offlineContacts();

public SortedContactCollection OfflineContacts { get; }

            var user = null;
            var onlineContacts = [];
            var offlineContacts = [];
            
            // Handle authentication - sign the user in.
            function onAuthCompleted(sender, e) {
                user = new Microsoft.Live.Messenger.User(e.get_identity());
                user.get_onlineContacts().add_collectionChanged(onOnlineContactsChanged);
                user.get_offlineContacts().add_collectionChanged(onOfflineContactsChanged);
                user.signIn();
            }
            
            // Responsible for updating the onlineContacts array to match
            // the User.OnlineContacts collection.
            function onOnlineContactsChanged(sender, e) {
                switch (e.get_action()) {
                    case Microsoft.Live.Messenger.NotifyCollectionChangedAction.add:
                        onlineContacts.splice(e.get_newStartingIndex(), 0, e.get_newItems());
                        break;
            
                    case Microsoft.Live.Messenger.NotifyCollectionChangedAction.remove:
                        onlineContacts.splice(e.get_oldStartingIndex(), e.get_oldItems().length);
                        break;
            
                    case Microsoft.Live.Messenger.NotifyCollectionChangedAction.reset:
                        onlineContacts = new Array(sender.get_count());
            
                        for (var i = 0; i < sender.get_count(); i++) {
                            onlineContacts[i] = sender.get_item(i);
                        }
                        break;
                }
            } 
            
            // Responsible for updating the offlineContacts array to match
            // the User.OfflineContacts collection.
            function onOfflineContactsChanged(sender, e) {
                switch (e.get_action()) {
                    case Microsoft.Live.Messenger.NotifyCollectionChangedAction.add:
                        offlineContacts.splice(e.get_newStartingIndex(), 0, e.get_newItems());
                        break;
            
                    case Microsoft.Live.Messenger.NotifyCollectionChangedAction.remove:
                        offlineContacts.splice(e.get_oldStartingIndex(), e.get_oldItems().length);
                        break;
            
                    case Microsoft.Live.Messenger.NotifyCollectionChangedAction.reset:
                        offlineContacts = new Array(sender.get_count());
            
                        for (var i = 0; i < sender.get_count(); i++) {
                            offlineContacts[i] = sender.get_item(i);
                        }
                        break;
                }
            }