GSM modems - sim card question

Hope this group can help. I have 2 Wavecom Fastrack GSM modems that I
want to use to send data between a PC and an electronic sign. I have
tried to use sim cards from my normal mobile phone, but these only
appear to be registered for voice calls, not data calls. What type of
sim card or plan do I need to make these modems work. The volume of data
transmitted will be very low, maybe about 2k twice a week, just to
update the messages on the signs.

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I wrote:

> As a general rule, you will need to call the SIM's data number
> to establish a data call. This will be a different number
> from its voice number, and likely cost you an extra monthly
> fee. Speak to your carrier.

Whether you can /make/ data calls from a non-data SIM is a
separate matter from the ability to receive data calls. You
might be able to make data calls from the voice SIMs of all our
Australian carriers, although Optus might be an exception. But
I'm not sure. It's a long while since I had any up-to-date
info.

An easy way to test is to try making a data call from the GSM
modem and SIM to a normal POTS (fixed landline) phone. If it
rings, it's a fair indication that you can. There's no way of
signaling the call type within the POTS system itself.

John

I wrote:

> ... last time I checked you could still get it to work if you
> asked for a V.110 ISDN connection to a voice number. It's
> worth trying. Your modem command to set the call type to
> V.110 is
>
> AT+CBST=71

I'd forgotten about possible use of the "single numbering
scheme" command facility. It's not something I've done myself,
and would depend on whether your carrier supports your making
data calls towards a GSM "voice" number.

It seems that you may be able to set up the default OTA call
type characteristics on the answering modem using the "AT+CSNS"
command.

AT+CSNS=4

sets the default incoming bearer up to "data" in situations
where the incoming bearer is not specified with the call
(otherwise the default will be "voice"). This is consistent
with my getting data calls through to voice numbers using
"AT+CBST=71" on the calling modem, since the bearer information
is undoubtedly passed through in that case.

Wavecom modems seem to offer the

AT+CICB=0

command as an alternative to provide this functionality -
setting up the default bearer type to "data" on the answering
modem.

So it's worth experimenting with "AT+CSNS=4" and "AT+CICB=0" on
the answering modem, as an alternative to trying "AT+CBST=71"
on the dialling modem.

Given your direct connection to a "dumb" display, you'd need to
make sure you can save any required answering modem settings as
defaults. This is especially relevant to Wavecom modems with
the recommended use of the "Wavecom reset", "AT+WRST" facility.

Please let us know how you go with all this.

John