Over the past two decades, telecommunications interception has developed into a major industry. Intelligence agencies and private organizations within all countries routinely intercept calls that may yield sensitive political, military or economic information.
The use of wiretapping has become so widespread, simple and uncontrolled that you must assume that records of your private calls and SMS end up in the wrong hands. Equipment for wireless interception of mobile phone calls and messages has become available at such low prices that it is deployed frequently even in comparatively small business conflicts. So using encryption to protect your privacy is the prudent choice.