what you heard,
" that people could be located by triangulation" is true in principle,
but not necessarily a threat to privacy. The important question is who has
access to what data.
Lets' first review the acronym soup associated with cell phones (or mobiles
as we call them in Europe).
GSM 'global system for mobile' communications is a global standard for mobile
phones, currently using 900/1800/1900 frequency bands.
In USA these phones are rare but available, often called 'world phones'
SIM card is personality module for a GSM mobile, which defines it's identity
(phone number, operator, and credit arrangements). For privacy
concerns it is good to know that SIMs can be bought two ways, as
prepaid or as subscription cards.
The latter requires that you give the operator your name and address, and often
a permission to run a credit check. The former is anonymous - same as cash.
SMS are like e-mail, but limited to 255 characters and sent from
mobile to mobile.
Like email, they were a spontaneous success, no one planned for:
GPS The Global Positioning System can determines position of the
receiver using three nearby satellites.
Acronym usually refers to use of 24 satellites controlled by U. S.
Department of Defense (DOD), but other countries are developing
similar systems. The idea itself dates back to the Sputnik.
IMEI - one more acronym -- important for privacy issue : Each GSM
mobile phone has a unique International Mobile Equipment Identity , a
16 digit number used to identify the mobile phone but not the network
subscriber using the phone.
This number is embedded into the phone and stays the same when
user changes a SIM, which identifies the network subscriber using the
phone. Currently, the number can be changed by an expert, but this
year we are switching to a new system to in which this number will be
indelibly hard-coded in the phone.
This is done to foil the industry of reselling stolen mobiles,
which is burgeoning in Europe.
Done with the acronyms, we can now look how it works and what is
revealed when you use a mobile.
We will skip many details, which can be found here
and focus on privacy:
On each call, be it voice or SMS, the IMEI of the mobile is sent to
He (operator is the phone company which sells you their SIM) knows
your position and uses that information e.g. to hand you over to a
different tower, as you are moving arond. Each tower has it's cell
(which is why it is called a cell phone) and using three nearby
towers, the operator can and does read your location. Operator does
not know who you are, if you are using a prepaid SIM. These days,
operator usually keep that information for himself
- but law enforcement can get it, as specified by incresingly less
and less transparent rules.
That (operator usually keep that information for himself) is likely
to change, as many services, (emergency, find nearby restaurant,
hotel, show me way-to ..) can benefit from these data.
When this data are released, provider of some such services, will know
where you are; he will than be able to customize his service.
Provider is gnerally different from the operator - it is a value-added
service - but operator can be a provider of some such services.
The way it is now, person whom you call, only knows your phone
number, ( caller ID is on by default )unless you block that.
Of course, large corporation can make private arrangements for
business phones they provide to the employees. Cab operators,
services, .. already do that - mostly using GPS so far, not mobiles.
!!!! However, if you switch OFF your mobil, no one can track you.
So, one should start worry about the 'Big Brother' when citizens are
ordered to keep their 'mobiles on' - or rather - when the off-switch
will be disabled.
On the other hand - it may be too late then - may be we should worry now.
The trade-off between security and liberty is very real.
Today, when worms and viruses are migrating from computer networks to
mobile phones, the whole issue is becoming interesting.
However, it is not the technology, but politics and policies,
which we should worry about first and foemost -but that would be
another great and complicated question.
Thanks for a great question.