RegisterFailed in case of IP to IP call (no proxy)

[Sentoj]

I am trying to register an Account object for IP to IP call as follows:

        Account account = new Account("sip", "", "127.0.0.1", 5060); // no password
        Phone phone = new Phone(account);
        phone.IncomingCallEvent += delegate (Call call) {
            Console.WriteLine("Incoming call.");
        };
        phone.ErrorEvent += delegate (Call call, Phone.Error error) {
            Console.WriteLine("Error: " + error.ToString());
        };
        phone.Connect(); // connecting

I get RegisterFailed. Does this wrapper (and linphone) support direct IP to IP without proxy? If so, can anyone please help me find the error in the code snippet above? (any idea on the SIP account parameters?)

Thanks,
Hisham