I tried in this way. I subscribed to that event who control the user status, its announcing me that user in Online. my code is:

void Nameserver_ContactOnline(object sender, ContactEventArgs e)
{
        Talk = messenger.CreateConversation();
        Talk.Invite(e.Contact.Mail,ClientType.PassportMember);
        Talk.SendTextMessage(new TextMessage(Msg));
        Talk.End();
        LogEvent("Contact online " + e.Contact.Name.ToString() + " " + e.Contact.Mail.ToString());
}

someone can give me a hint ? maybe i do something wrong because message wasn't sent. thanks.