    Interesting article about the danish phonecard system, typed and 
    translated from a year round-up issue of Computerworld.  


    CARD CHEATERS ARE STOPPED HERE 

    You probably don't know but you and your phonecard are being watched 
    closely when you're making a call from a cardphone.  The phone holds 
    on to your card when you insert it into the slot and while you're 
    speaking, the computer in the phone is checking and registrering the 
    invisible data on the magnetic strip of the card.  Everything is 
    registrated:  The number of the card, the amount you're talking for, 
    the time of the call, how long it is and the first digits of the 
    called number.  

    The computer makes sure that the card isn't used up and the phone 
    will immediately eject the card and disconnect the call, if the files 
    of valid or black-listed cards show that your card is stolen, a 
    forgery or in some other way unusable.  

    The computer is pretty velinformed.  At least once a day it's updated 
    by it's big brother, PMS 200, a central computer.  PMS 200 stores the 
    numbers of all cards, even before they are put in circulation.  At 
    this moment PMS 200 is keeping track of approx.  five million cards, 
    and it follows them through their entire lifetime.  All data about 
    calls is kept for 30 days, so the technicians of the phonecompany can 
    track suspicious cards.  

    However, cardphones aren't infallible.  Should something go wrong, 
    for instance a phone looses it's speaker or chokes on a card, it will 
    immediately tell it's other big brother PMS 100, which is constantly 
    keeping track of the health of the phones.  
