Data over normal GSM call

Mikko Rauhala mjrauhal at
Tue Apr 8 17:26:11 CEST 2008

On ti, 2008-04-08 at 17:16 +0200, Tilman Baumann wrote:
> Maybe CSD is billed like a voice call. I never used it, but i don't 
> remember any special charges for that.

Doubtful for the US "drop your pants and bend over, please" carriers'
"minutes"; I presume the original poster was in this situation from
his .edu account and mention of AT&T.

Here in Finland we're mostly billed by minute (though there are
_optional_ US-like plans), and CSD calls indeed cost pretty much the
same as voice calls. I presume the situation may be similar in many
other (esp. EU) countries as well, which is good for us if we want to do
eg. those encrypted phone calls or cheaper international calls via
VOIP/CSD, but doesn't help the original poster.

> The Wikipedia article about CSD has some hints about running voice 
> modems via GSM too.

A quick glance finds mostly mentions of 1st gen analog mobiles having
been used with modems, and notably "At the same time, the speech
oriented audio compression used in GSM actually meant that data rates
using a traditional modem connected to the phone would have been even
lower than with older analogue systems."

Mikko Rauhala <mjrauhal at>
University of Helsinki

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