The NSA has developed its own encrypted VoIP protocol using Google's Android operating system. The phones, designed for US government staff, are password protected and use certificates to authenticate other handsets.
The NSA looked at SSL VPN as a standard and left no stone unturned in exploring commercial SSL VPN for mobile, but found utter lack of interoperability across vendor products. Salter said NSA also was frustrated with the lack of interoperability in Unified Communications Systems (UCS) products, noting that buying one piece often meant buying several others, there being little evidence of multi-vendor interoperability. So with some frustration, NSA changed to go with an open-source Session Initiation Protocol (SIP) server for the present. CIO