Recommendations for a data-only GSM/UMTS device in USB stick ff

Michael Sokolov msokolov at ivan.Harhan.ORG
Sun Nov 20 07:26:41 CET 2011

David Pottage <david at> wrote:

> I think you will find that it is imposible to make data calls to an
> analoge modem. The reason is that GSM and it's sucessor standards are
> inherently digital, and are derived from ISDN telephone standards, so
> nothing in your phone or in the phone network will create tones that
> will be understood by an analogue modem.

There is a gateway somewhere in the network, probably at the point
where the mobile network connects to the old PSTN, that does the
trick.  Just like for voice calls some gateway has to convert between
the 9600 bps or whatever codec is used in GSM and the classic 64 kbps
of the wireline world, that gateway is apparently also capable of
acting as a voiceband modem emulator, handling a data call on the GSM
side and doing V.32 or whatever modem tones on the wireline side.

I have personally used this feature back in 2004-2005 timeframe.  I
had a Mot V66 phone on T-Mobile USA, just like I do now, and I was
able to connect the data cable to my phone, run minicom or similar on
the laptop, and type ATD<number>, where the number was that of a land
line with a USR Courier V.everything modem.  It worked, connected at
9600 bps.

I want to do the same thing again.  Hopefully whatever gateway makes
it work hasn't been dismantled, although I will likely be its sole

> Given your other requirements for off the shelf hardware, I think your
> simplest solution would be to buy a mobile phone with a data port, and
> learn how to use that port as a GSM modem. For example I used to work
> for Nokia, and I know that with their phones, if you put them into "PC
> Suite mode" they will respond to AT commands on their serial/usb ports
> and let you do dial up internet to your ISP, or any other phone number.
> You may find that your current phone does what you need.

Yes, that's exactly what I used to do, using an identical phone.  But
it's a very clumsy solution, the data cable is bulky and inconvenient,
and the Mot V66 makes it impossible to connect the data port and
external power at the same time.

I was wondering if I could take one of those cell modem USB sticks
that a lot of people use nowadays for Internet on the road, and talk
AT commands to it.  Then I could try doing the ATD<number> from it: if
it works, it would be a lot more convenient than using a phone and a
data cable.

The data-only cell modem devices in the USB stick form factor have the
additional advantage of being completely batteryless, taking power
from the laptop's USB port and nowhere else.  It's a little easier for
me to tolerate using a device whose GSM firmware I have no source for
if that device is incapable of having any of its circuitry powered up
except during those brief moments when I plug it in.


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