You can't trust government!
Government security workers have used security information to enrich themselves in the U.S.A.
Whilst those with intimate familiarity in the telecommunications industry have known what governments routinely do, surreptitiously, the current level of chatter is very healthy for more and more people are becoming sensitive to eavesdropping/monitoring done by governments.
RedPhone 0.1(voice)[uses ZRTP by Phil Zimmermann] and TextSecure 0.3 (text) are amongst several answers for Android users and defy government monitoring.
Secfone (software), Rohde & Swartz (Bluetooth hardware) and SnapCell (hardware) are others.
Using specific cell phones to call specific numbers stops governments building a database of contacts and using a pair of hand-phones as one-way communicators or split communications (A cell used for talk only to cell B; cell C used only to talk to cell D [A & D are one end and B & C are the other end]) is very effective, more so when they are paired using different carriers.
Developing countries, China excluded, definitely don't have the technology to beat these and even the U.S. capabilities are challenged.
Cell hygiene is essential (clearing registers, powering down periodically), Carrying cells across borders allows Plod and company to gather information such as the IMEA which can be used to build contact information.
Using calling cards is ineffective as all numbers are recorded, although dedicating one card to one called number increases difficulty in building contact databases (and not using different cards sequentially from one number).