Data over normal GSM call

Harald Welte laforge at
Thu Apr 10 19:34:59 CEST 2008

On Tue, Apr 08, 2008 at 10:22:10AM -0400, Dan Staley wrote:
> Does anyone know if it is legal (in the standard TOS) with providers
> (such as ATnT) to send data over a normal phone call?

this is not possible, since regular voice calls for GSM are not
bit-transparent, i.e. the voice signal is coded and potentially re-coded
(transcoded) a number of time between the calling and receiving party.

Data calls over GSM are done using CSD.  They also use quite a lot more
error correction than voice calls.

- Harald Welte <laforge at>         
Software for the world's first truly open Free Software mobile phone

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