“The company’s system reads an anonymous identifier that mobile phones transmit and can then track their movements [Demo here].

The approach will be useful for research, security and improving services in environments ranging from train stations to refugee camps.

[...] Mobiles are assigned a temporary anonymous number by the network called a temporary mobile subscriber identity, or TMSI, which the phone periodically transmits to advise of its location. As the phone moves through the different regions served by different base stations, that number changes. Path Intelligence’s approach, called FootPath, directly detects that TMSI transmission from phones. No access to the mobile networks themselves is necessary, so the information that they glean is specific to a user, but completely anonymous.

[...] It has been approached by humanitarian workers in refugee camps, where a lack of central planning means it is often difficult to site services such as clinics where they can be best used.
The system will also be useful for researching the layout of, for example, train stations”

BBC article: mobile tracking reveals spending. Wednesday, 8 October 2008, UK