DN> That's not the way I heard it. Every radio transmitter is unique in
 DN> the way it keys up, comes up to power and stabilizes on frequency.
This is a second type of fraud prevention-completely unrelated to the one
discussed earlier.
 DN> This is like a fingerprint. No two transmitters are exactly the same.
 DN> Authentication is a record of your cell phone's signature. Every time
 DN> you make a call (perhaps every time you turn it on?) the cellular
 DN> carrier compares the signature your phone has with the database
But this system fouls up all the time-especially if the customer has a
problem with the phone and it gets serviced, thus changing the transmitter's
so-called "fingerprint".
 DN> signature. If they match, fine. If not, your call will not go through.
 DN> Presumably, if you have repairs done to your phone that change this
 DN> fingerprint, your carrier will have to establish a new database enty
 DN> for your phone. 
Actually, this system screws up all the time.  Many carriers "pretend" to
be using it, but in actuality it is just a ruse.  The most effective ways
of stopping cloning fraud today involve the "challenge" method (see previous
message) or even simple anti-fraud programs running on the switch.  One
clever program notes where calls are placed by individual phones.  If
another call is placed 5 minutes later in a cell 50 miles away, either the
phone has been cloned or someone has perfected a "star trek" like trans-
porter!   Or even the simple (and stupid) user who has gone to a "cellular
extension" type place and turns both phones on at the same time-one being
in the user's car and the other being in the wife's car which happens to
be on the other side of town.  OOPS, how can that one phone register in two
cells miles apart at the same time??
... Computers can do that?! - Homer
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