On Thu, 27 Oct 2005 12:22:56 +0100, Dave Brown
<dave@REMOVETHISFROMADDRESSdbws.net> wrote, quoted or indirectly
quoted someone who said :

From what I have read the way tracking works is this:

1. every phone has a unique serial number chip. You can move it from
phone to phone. It also carries your personal phonebook.

2. As you wander around perhaps 3 different stations can hear the
phone bleating for attention. They each measure signal strength and
triangulate to determine the phone's location and hand off the phone
to the closest tower.  Presumably some advanced system might do it the
way GPS does by the phone measuring the time a given tower's mark took
to arrive. The stations don't know of the phone's existence until the
roamer turns it on.

3. Internet providers then discover foreigners roaming in their
territory. They put them in their database, and share data with other
providers so others know the whereabouts of a give serial number chip.
They find out from the home billing company just what services to
provide.

4. Billing is obviously hairy, but in essence means timing calls and
sharing that data with the home billing company and with everyone
getting a cut of the billing pie.