I'll be upfront, I'm a little biased... my dad wrote ZRTP and helped design the encryption on the Silent Phone app. There are a number of reasons I trust it. On

I'll be upfront, I'm a little biased... my dad wrote ZRTP and helped design the encryption on the Silent Phone app. There are a number of reasons I trust it. One is that the user is involved in authenticating the call. Most other encryption apps bury that authentication in the settings, allowing you to not worry your pretty little head about it. I trust both the good intentions behind the design as well as the implementation.