Cell phones have become omnipresent ; no one even spares another glance at someone hurrying along the sidewalk and seems to be talking to his own self. Of course he is using the handsfree and chatting to his contact who may be on the other side of the globe for all we care.

Considering that we use a cell phone even in the presence of a land line now that call rates are mostly on par, perhaps we should be evaluating security concerns about this risk. While it is common knowledge that authorities have had access to our calls, we were satisfied by the fact that this capability could not be mis-used. Even the authorities needed to get permission from a court of law with specific reasons for their wanting to do so. (Of course I assume that you did nothing to piss off the CBI or an agency on that level. In case you already did then God Help You, those people have technology which would leave you dumbstruck, as well as a free hand to use it when they think necessary).
With landlines, it was difficult to tap the phone, especially since they would need to put a physical bug on the wires which meant access to the lines and a kind of sophistication which would not be easily learnt. However with things going wireless, it becomes easier. Interception devices are now available that can record conversations. If you suspected the presence of these things and sent confidential data by SMS, then it was in vain since these things are powerful enough to get these too. To add salt to the wounds, the conversations and messages are neatly indexed and stored in a data base for future reference. These interceptors are cleverly disguised in forms of briefcases, suitcases or perhaps even a rugged outdoor case (cant be smaller than those since a particular size is required to be effective, maybe with more advances in technology we will have smaller ones.) While they do have their own power units which could last for some time, its better if you gave them a power supply since spying on someone is not something you do for an hour or two. Days of patience are required before you can have results. Don’t worry about power points though, these things are designed to be inconspicuous; you are ready to go even with a car cigarette lighter point.

These portable interception devices cost someplace between 20,000 dollars upwards depending on the features but they do come with a guarantee of getting you behind bars if you are not a law enforcing agent. Another option is to use the cell phone cloning or SIM card cloning method. However this requires you to have access to the device for some time.