Playing on mobile users' fears of commercial and government surveillance, two companies are building a phone they say is designed to protect privacy. The joint venture between smartphone manufacturer Geeksphone and encrypted communications provider Silent Circle will unveil the new device called Blackphone at the Mobile World Congress show in Barcelona next month.

Blackphone will run an Android-based OS called PrivatOS that the companies claim will allow users to communicate securely. According to them, users will be able to make and receive secure phone calls, exchange secure texts, exchange and store files securely, engage in secure video chats, browse privately, and access the Internet anonymously through a VPN (Virtual Private Network) connection.

Details about the technology used and other implementation aspects are not yet available and Geeksphone declined to release any additional information ahead of Mobile World Congress. However, giving Silent Circle's involvement, it's reasonable to assume that some of the company's existing apps and services will be integrated into the new handset.

Based in National Harbor, Maryland, Silent Circle offers subscription-based encrypted voice calling, video chat, text messaging and file transfer services through Android, iOS and desktop apps, some of which have had their code released publicly.

The apps use end-to-end encryption technology based on open cryptographic standards, some designed by people who founded Silent Circle like Phil Zimmerman, the company's president and creator of PGP and ZRTP, and Jon Callas, the company's chief technology officer. Both Zimmerman and Callas are members of the new Blackphone team.

Silent Circle operates servers in Montreal and Toronto and according to its website has plans to open a new facility in Switzerland, which is where the new Blackphone joint-venture is based.

If the new phone does use Silent Circle's services, it's not clear whether users will have to pay a monthly or annual subscription to use them. There's no estimated price or general availability date for the smartphone itself either.

While adding encrypted communications is important, developing a truly secure phone takes more than that. There is currently no information about the hardware components used in Blackphone, some of which, like the baseband processor that controls the radio functions of the device, have their own low-level proprietary firmware.

Security researchers have warned in the past that potential vulnerabilities in baseband firmware can undermine the application-layer security features of the OS.

Hopefully Silent Circle will display the same level of transparency for Blackphone as it did for its existing apps and will explain how the device was designed, if and what third-party security audits have been performed and explain in more detail how PrivatOS differs from Android.

Based in Madrid, Geeksphone also prides itself on creating mobile telephony products based on open standards and open source software. So far the company has manufactured mobile phones that run Android and Firefox OS.