Silent Circle was partially founded by Philip Zimmermann, so that's supposed to lend some credibility to the operation. The company, and PZ in general, still operate on the premise that trust in them should be enough for anybody, so the operation will be opaque and the source closed.
I really respect a lot of what Zimmermann has done, but we're finding out more and more that our trust in institutions was ill placed. I don't think his model works in our current world. Finding out in twenty years that Silent Circle was an NSA front wouldn't really surprise me that much, despite Zimmermann's involvement. "Trust me, I'm one of the good guys," doesn't fly anymore.