If you're worried about the NSA listening in on your smartphone, Silent Circle's "Blackphone" may be the last best hope.

First announced in January, the Android-based phone goes on sale before the start of July for $629, according to NBC News.

While the price is a bit hefty, it comes with impressive features, including fully encrypted voice, text, and video calls, and a virtual private network that anonymizes web surfing — all built on a custom version of Android.

Demand for such a device certainly ramped up after Edward Snowden began leaking top-secret documents detailing NSA surveillance programs, but Silent Circle had been working on the device long before.

"We did this because there was a problem that was not being solved: secure communications," CEO Mike Janke, a former Navy SEAL, told AFP in January.

With Janke leading the company, Silent Circle's team includes a number of cryptographic experts. including Phil Zimmermann, the creator of the widely-used PGP (Pretty Good Privacy) standard.

The company has taken great pains to ensure it could not give up user data, even if compelled to by a government. While many U.S. companies receive controversial national security letters forcing them to share customer info, Silent Circle is incorporated in Switzerland and has Swiss data centers.

But the main thing that sets the security of the phone apart is that the encryption itself resides only on the handset. While encrypted data passes through the company's servers, the individual keys necessary to unlock and read the data are only on the phones.

Basically, if Silent Circle was forced to hand over data, all they could give up is a bunch of encrypted gibberish.

"There is no such thing as a completely secure phone," Janke told AFP. "Nothing is going to protect you from your own behavior. But out of the box, this phone does a lot of things to protect your privacy."

Silent Circle isn't the only company to come up with such a device. Boeing unveiled their own version of a "black" phone in February that had a "self-destruct" feature.