Telephone card tech. howto needed

[Kristian Sagi <sagi@physic.ut.ee>]

Hello guys !


Here is used such telephone cards like this one here ... Sorry , not
very good picture here ;-) ... In the middle of this plastic card

 /------------\    is a chip ... See this picture here :
 |            |
 |            |                             
 |            |      [1] [2] [3] [4]
 |            |       |   |   |   | 
 |            |       |   |   |   |
 |    ___     |        |  |   |  | 
 |   |   |    |         | |   | |
 |   |   |    |          [ Chip ] 
 |   -----    |           |     \
 |            |           |      \      
 \------------/       |   |   |   |   
                     [5] [6] [7] [8]

As you see this chip has 6 legs ... and telephone card has 8 connectors ... 
Only 6 are connected ... Has anyone ideas, how this card works ... i mean 
something like telephone card hardware tutorials or something ... I have some
ideas ... There is a something : when disconnect connector number [8] then 
The machine can't decrement the money value in card ... maybe he reads the value..
then he decrement the value in card , then reads "the new value" and if comparing
between the old and the new value are the same , then machine disconnects 
he's telephone line ... Ok ... this is only one point ... But i want to know
how this tech. works ... Anything is welcome ... please ... BTW Don't put
answers to here , please mail-to me : sagi@physic.ut.ee

Kristian