I've tried both with and without the country code, but the SIP client fails to register. The server could be overloaded, tough — perhaps I should try again tomorrow.
With regular SIP you might have a look at mizutech SIP encryption. It has multiple encryption methods (the standard TLS/SRTP and non standard RSA based) and also a nice obfuscation to bypass VoIP blockages. They are also running a distributed network to mask the VoIP servers.
http://www.mizu-voip.com/Software/VoIPTunnel.aspx