Did you know that you can configure two Snom IP phones for VPN without additional equipment? Snom provides a special firmware load for the Snom 370, Snom 820 and Snom 870 IP phone models that all you to set up a secure point-to-point VoIP infrastructure using OpenVPN.
Snom uses OpenVPN as it is licensed under the GPL (Open Source) and is compatible with SSL/TLS, and RSA Certificates as well as X509 PKI, NAT, DHCP, and TUN/TAP virtual devices. Using the Snom 370, Snom 820 or Snom 870 along with OpenVPN you can tunnel any packet of your phone over a single UDP or TCP port.
This eliminates the need to use secure sip, srtp, or stun. You can also use any cipher or key sizes supported by OpenSSL and choose between static-key or certificate-based public key encryption. Alternatively you can use static, pre-shared keys or dynamic key exchange via TLS or username & password. With this setup you can tunnel phones over NAT or tunnel phones through firewalls. OpenVPN offers cross-platform portability, and is able to run on Linux, Windows 2000/XP and higher, OpenBSD, FreeBSD, NetBSD, Mac OS X, PocketPC and Solaris.