Recent reports in the Washington Post indicate that Skype is no longer the service of choice for people who value their privacy in conversations over the phone or the computer. The Post reports that since being acquired by Microsoft, the service has changed its network architecture and made communications more open to government spying. This may be of particular interest to people who use relatively low cost Internet connections to make phone or video calls internationally.
The key to secure telephony and video communications appears to be ZRTP, a protocol developed by yes, once again, Philip Zimmerman, which basically provides end-to-end encryption of telephone communications over the Internet via SIP.
At this point, it would appear that people interested in the privacy of their phone conversations have two potential alternatives.
Those seeking a prepackaged version of SIP telephony encrypted with ZRTP might want to investigate iCall.com.
Alternatively, those with a more do-it-yourself attitude can sign up for an SIP service such as CallCentric. Bear in mind that one has to pay a little more to talk to “real phones” as opposed to just other computers. It may also be necessary to purchase a phone number if one wants to receive calls from “real phones.”
Having signed up for the service, one then needs to buy or download a software client for whatever phone or computer one is using. It is important to ensure that whatever client one obtains, it supports ZRTP. Some cross-platform examples include Jitsi, and Linphone (some versions). SFLphone is available for Linux, and Groundwire for iPhone (with an in-app purchase).
The final thing to remember is that encrypting a call with ZRTP only works if the guy on the other end is using it. A good software client should give an alert if this is not the case.