From the article:
If you’re making a phone call with your iPhone, you used to have two options: Accept the notion that any wiretapper, hacker or spook can listen in on your conversations, or pay for pricey voice encryption software.
As of today there’s a third option: The open source software group known as Open Whisper Systems has announced the release of Signal, the first iOS app designed to enable easy, strongly encrypted voice calls for free. “We’re trying to make private communications as available and accessible as any normal phone call,” says Moxie Marlinspike, the hacker security researcher who founded the nonprofit software group.