TM> HOw does this work?  I was reading about it in the new episode of Time
TM> Digital and they were talking about a # that is stored in the service
TM> providers data base but is never broadcast over the airwaves?  How do
TM> they check it then?  I mean if it's never broadcast it can't be checked
There are currently two techniques being implemented right now. Both with 
great success, but one method will likely become the standard while the other 
will end up being a useless novelty for the time being.
Method one involves RF fingerprinting, which is where the cell company has a 
database of your telephones RF characteristic stored on file. Each phone has
a slightly different waverform (the measurement is sampled at power-up).
and even phones of the same brand, same model, made on the same day, by the 
same guy on teh assembly line, with the same batch of components, etc.. etc.. 
the fingerprint or waveform will be sligtly different.
the second method iof authentication involves a "smart card" type system
(actually no smart card is used, the chip is just built into some of the 
ewer
phones).  This technique (likely the one that will win out as the better 
system for now).. involves the cell site sending out a numerioc sequence 
called the "challenge". The cell phone receives the numbers, runs it through 
an algorithm and a "response" set of numbers will be issued.  If the cell 
ite
determines that your phone generated the proper response then your are 
authenticated and your call may proceed.
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