Unable to receive GSM Data Calls


I am trying to set up the modem to answer in data mode (NOT GPRS), however I am not having much success.
The modem answers, but does not begin the handshaking whistles, etc. when it answers. It just answers in silence.
I have wired up the modem to a PC for testing, and have made the following connections to simulate a null modem connection:

Shorted pins 1, 7, and 8 (CDCD, CDSR, CDTR)

Shorted pins 11 and 12 (CCTS, CRTS)

I have configured the modem with


What else needs to be done ?

I have tried the modem with SIM cards from Telstra and Vodaphone (Australia)

I can make outgoing GSM data calls but the modem does not receive calls, ie. it answers but does not initiate a data session.

Additional Info:

The modem appears to be identifying all calls as VOICE calls. Is there any way to get the modem to ignore the call type and answer all calls as data calls ?