Synchronizing SIP agent events with UI

ChatControl.cs

public class ChatControl
{
  private void client_LoginStateChanged(object sender, EventArgs e)
  {
    if (client.LoginState == LoginStateEnum.Logon)
        client.Messanger.IncomingMessage += Messanger_IncomingMessage;
    if ((client.LoginState == LoginStateEnum.Logoff || client.LoginState == LoginStateEnum.LoginError) 
        && client.Messanger != null)
        client.Messanger.IncomingMessage -= Messanger_IncomingMessage;
  }

  private void Messanger_IncomingMessage(object sender, PagerEventArgs e)
  {
    ChatMessInfo mess = e.Body;

    List<ChatMessInfo> chatMessages = null;
    if (!conversations.TryGetValue(contact, out chatMessages))
    {
        chatMessages = new List<ChatMessInfo>();
        conversations.Add(contact, chatMessages);
    }

    chatMessages.Add(mess);
...

InstantMessengerService.cs

public class InstantMessengerService : IInstantMessangerService
{
	private SynchronizationContext _syncCtx;	
	public event EventHandler<PagerEventArgs> IncomingMessage = delegate { };

	public InstantMessangerService(Account chatAccount)
	{
		_sipUserAgent.IncomingMessage += OnIncomingMessage;
		_syncCtx = SynchronizationContext.Current;
	}

	private void OnIncomingMessage(object sender, PagerEventArgs e)
	{
		try
		{
			_syncCtx.Post(delegate
											{
												// read and parse msg
												ChatMessInfo chatInfo = new ChatMessInfo(StringExtensions.ExtractUid(e.From), docx.DocumentElement);
												IncomingMessage(this, new PagerEventArgs(e, chatInfo));
											}, null);
		}
		catch (InvalidOperationException)
		{
		}
	}