Question : Connection between cell modem and standard modem

Hello,
I can't seem to be able to connect to a cell modem with my standard modem.
I'm trying (for testing purposes) with Hyperterminal: I give my standard modem the ATDT command, then I see on the cell modem terminal the "RING" message. At this point I type ATA to tell the modem to answer, but the connection is not set up, and after a while the standard modem just hangs up :(
BTW the other way round is working: that is, if I say the cell modem to dial, and the standard modem to answer, the connection is set up (at 9600baud).
Does anybody know what's going on? Consider I'm total newbie to wireless programming, I just thought I could use a wireless modem like any other modem, but this doesn't seem the case... any introductory links would be greatly appreciated too!
Thanks.

PS The cell modem I'm using is Sony Ericsson GM29.

Answer : Connection between cell modem and standard modem

Ok here's the deal..

First there is not actually a modem inside your GM29 (or any other GSM or CDMA phone for that matter).

Instead your carrier has a device called an Interworking Unit somewhere on the network, this device is essentially a bank of modems, data from your phone is sent to the Interworking Unit as a digital data stream and vice versa.

When you make an outbound (GSM to PSTN) call the phone knows you're making such a call, selects the appropriate bearer and the modem in the Interworking Unit actually 'dials' your PSTN modem.

The other way round is not so simple, the network is configured to make a voice call to your phone when the standard voice number is called, in order to get the Interworking Unit to answer and make a DATA call to your handset you need to somehow tell the network that's what you want to do.

And yes I'm absolutly positive