The purpose is the same
with regard to e-mail:
"Silent Circle consists of four applications: Encrypted Email, Encrypted Mobile, Encrypted VoIP, and Encrypted Text. The Silent-Circle client encrypts the traffic before sending it to our servers using the mobile devices Wi-Fi or data side of the cellular connection. Our servers then forward the packets onto the appropriate remote party."
The purpose is to prevent someone who intercepts the packet(s) from reading the content, of course.
What is unclear to me is why the packets encrypted by the mobile client are sent to the Silent Circle servers instead of directly to the intended recipient, whether for e-mail, voice, VOIP, or SMP.
Other than that, yes, PKWare currently doesn't have an app which runs on smartphones and tablets that will encrypt and compress a file, only one that will read them.
