Mobile phones are commonly used to collect location data. While the phone is turned on, the geographical location of a mobile phone can be determined easily (whether it is being used or not) using a technique known as multilateration to calculate the differences in time for a signal to travel from the mobile phone to each of several cell towers near the owner of the phone.
The movements of a mobile phone user can be tracked by their service provider and if desired, by law enforcement agencies and their governments. Both the SIM card and the handset can be tracked.
China has proposed using this technology to track the commuting patterns of Beijing city residents.
In the UK and US, law enforcement and intelligence services use mobile phones to perform surveillance operations. They possess technology that enables them to activate the microphones in mobile phones remotely in order to listen to conversations which take place near the phone.
Hackers are able to track a phone's location, read messages, and record calls, just by knowing the phone number