Re: ISDN + GSM
If you find the correct drivers for your modem, you probably can use your GSM as a PPP or SLIP modem. PPP is a protocol for sending IP-packets over serial lines. When you make a connection with your gsm, you have a direct serial line so you probably can run any kind of protocol over it!
When you're using a gsm it is possible that you have to use a specific driver to be able to enter the PIN-code. I'm not sure about this when you're using a normal consumer gsm. I only have experience with embedded gsm's where the only interface is the control uart.
And when you want to write a driver/application which talks to the modem directly you can do it like this (you can easily test in using hyperterminal!!!):
Open a serial Port (preferably the one connected to your gsm/isdn modem ;-))
Check communication with the modem by sending "AT"
Modem should respond with "<0x0D><0x0A>OK<0x0D><0x0A>"
(in hyperterminal you won't see the <0x0D><0x0A> since they are Carriage Return and Line Feed characters)
You can send all kind of controll commands to your gsm/isdn modem
see
https://www.traud.de/gsm/atex.htm for a reference
or search google for "AT Commands"
Some commands i use for GSM are
(all responses are enclosed by "<0x0D><0x0A>"):
ATE1
Now you see what you send, Echo back
ATE0
Now you don't see what you've send
AT+CBST=71,0
The answer should be "OK"
this puts the modem in data mode
Should we enter the Pin Code
AT+CPIN?
when the answer is "+CPIN: SIM PIN" then the pin code isn't inserted yet
AT+CPIN="xxxx" enters the pin and the answer should be "OK"
when the answer is "+CPIN: READY" then the pin code has been inserted
now we can dial out with
ATD+0123456789
"CONNECTED 9600" means you're connected with a 9600 baudrate.
"NO CARRIER" means the other side is no number (or a GSM which isn't registred to the network.
"BUSY" means the other side is making a call
...
Just install google on you PC and search for more information
And use Hyperterminal to try your stuff