A phone that is switched on can be located. The knowledge that you (or at least your phone) were in a particular place can be either positive or negative depending on the circumstances.
Mobile phones can be used to locate you and your companions in a particular place because your mobile is a tracking device when it is switched on. This information is kept by the provider and can be accessed in real time or after the fact. If your work is unpopular with the authorities this can make you very vulnerable - but one benefit of this is that your phone may provide an alibi to show that you were not elsewhere. Commercial services are now available that will allow you to track a mobile phone for a small fee from a website.
For a mobile phone to be able to communicate with the network, the server keeps track of which transmission mast your phone is connected to. A phone cell is made up of several masts and the information they transmit is used by operators to determine the approximate location of the actual phone. In large cities this can locate your phone within a couple of streets. This is occurring all the time your phone is turned on whether it is used to make calls or not.
To understand the sensitivity of mobile phone communication its worth bearing in mind that it is much harder to use a mobile phone anonymously than it is to surf the internet anonymously.
To undertake surveillance of phone conversations and SMS text messages, governments have to work with the mobile operators and service providers.
However monitoring and surveillance of mobile phone use is relatively easy through;
In some countries it is relatively easy for to get access to call and SMS records through;
Surveillance agreements might be in operation between your government and the telecoms operators in your country, so if you are working in a sensitive area be sure you understand as much as possible about surveillance agreements in that area. Governments have been known to work with mobile operators to do searches of call and SMS records for key terms.
In some countries the mobile phone network has been shut down by the authorities during election periods. For example, in response to the effective use of text messages to communicate with and mobilise supporters by the NGO Kinijit after the contested election in Ethiopia in May 2005, the government shut down SMS services. The services were only restored in 2007.
Mobile phone conversations are not encrypted and it is currently expensive to encrypt calls - however these tools are expected to become cheaper over the next few years. Conversations between Skype and mobile phones are also not encrypted.
Software can be installed remotely without your knowledge and then the phone used as a microphone/bugging device. A commercial version that can listen to conversations in the region of the phone is also available for purchase although it does not include remote installation. Anyone who had access to your phone could install such software.
Without installing any software a phone can also be set to work as a microphone by setting automatic call pickup and disabling a ring tone - by this means someone can call a remote phone and listen in to whatever is going on in its vicinity.
If the account you have with a phone company is a monthly account, a record of all calls made and received with the operator is kept and can be accessed long afterwards. Records held include billing, which services were used, where you were when making or receiving calls, numbers called and the numbers from which you received calls.
It is possible in some countries to obtain a pre-paid SIM card without providing any personal information but this is becoming increasingly difficult. For added security, it may be advisable to pay with cash and choose an outlet not covered by CCTV.
Using a credit card to pay for your mobile phone will also create a data trail to you, which you may want to avoid.