The FBI makes another anti-privacy declaration, following the theme of the past few years. This is another reason why it’s important to encrypt your sensitive calls to protect the content of your messages. However, as long as your phone is broadcasting to cell towers, its location can be determined. Switching your phone to Airplane Mode and using a WiFi-based encryption protocol to place calls, send texts, or chat, will help protect your words, but will not necessarily obscure your location or your metadata (who you’re talking to, when, where), which is the foodstuff of mass surveillance.
Every step you take to regain control of your privacy, however, is helpful. Taking steps to make mass surveillance uneconomical is an important way for us to exercise our constitutional rights and resist government intrusion into private life. Protecting free speech (I) and privacy (IV) is one of the most patriotic things that we can do.
Unless you’re the rare target of sophisticated government-sponsored malware (in which case you have bigger problems), powering off your phone should be sufficient to prevent transmission. Remember that even then, your uptime and downtime can be recorded, and if you tend to power off your phone at a specific time or place each day, that can be telling as well. Warrantless wiretapping policies implemented through the Patriot Act following the hysteria of 9/11 make much of this possible without permission from the courts, producing strongly negative chilling effects on speech and activity.
Finally, public surveillance cameras and video analysis using facial recognition software can identify people quite easily, so even without a phone, you can still be tracked–but every privacy measure you take makes tracking much more difficult and costly. This is yet another reason why many organizations, such as the Electronic Frontier Foundation (EFF), call for greater restrictions on government spying and law enforcement powers, to protect citizens’ privacy. Unless police serve a legitimate warrant, where we go, whom we talk to, and what we do, should remain our personal business.
edit: more info on rogue cell towers here