http://arstechnica.com/tech-policy/2014/05/photos-of-an-nsa-...
The problem is that who orders a Blackphone is not completely private and it is a sign that those people have something they want to hide and there isn't that many of them.
You almost need a private way of sending Blackphones so that the NSA doesn't know who is getting which phone and then if there is a enough volume of Blackphones you should be okay.