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From: hpa@casbah.acns.nwu.edu (Peter Anvin)
Newsgroups: comp.dcom.telecom
Subject: Re: Payphones and DTMF Dialling
Message-ID: <15648@accuvax.nwu.edu>
Date: 23 Dec 90 09:06:34 GMT
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>What I would like to know is: How do the American and Swedish telcos
>avoid fraud of this type? (They are the only two countries I
>personally know to have DTMF payphones. Comments from elsewhere are
>also welcome.)  Is it possible to use a tone-sender to dial from a
>payphone in USA or Sweden or elsewhere?

Swedish payphones (or, in fact, any Swedish phone with the proper
equipment installed) have access through the phone line to a pulse
signal sent out for each marking period = 0,23 SEK.  In other words,
although I have not tried it myself, I presume anyone could use a
tone-sender on a Swedish payphone, but it wouldn't help: you would
have to feed it coins anyway!

Televerket (Swedish Telecom) sells a "COCOT phone" to anyone that
wants one, it is just to plug into a regular Swedish four-prong phone
jack.  (By the way: all the four RJ11 wires are mandatory in Sweden
and are supported by the phone network: there are TWO
twisted-pairlines (for a total of four wires) in the local loop to
each line.  Maybe that has something to do with it.

Further note of interest: You have to feed a Swedish payphone its
minimum fee (the payphone fee for two marking periods, usually two
SEK) before it gives you dialtone (but you dial the number at the
dialtone).  Therefore, it costs you two SEK to call a "toll-free" 020-
number from a payphone.

Here in the USA, it seems like the amount of toll to pay is similarly
controlled from the switching office, except for local calls, which
are untimed anyway.  Illinois Bell's payphones give you a digitized
voice telling you how much you should put in the slot and which warns
you when you are about to run out of money.  Doesn't sound like
something run inside the phone, IMHO.


H. Peter Anvin +++ A Strange Stranger +++ N9ITP/SM4TKN +++
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