I have used a setup a little like yours; a Palm Vx and a Ericsson T39 phone. I know it's not the same, but maybe it will help you anyway.
First, create a 'Connection', from Prefs:
-> New
Name: GPRS //The name of the connection, used later.
Connection Method: IrCOMM to Modem //The modem is in the phone
Dialing: TouchTone //Don't know
Volume: Off //Sound ?
-> Detrails
Speed: 115.200 bps //Communications speed
Flow Ctl: Automatic
-----
In 'Network', Prefs;
Service: 'Your service provider' // Used by the palm for writing 'Dialing 'Your service provider'..'
User Name: 'Name' //Ask your service provider
Password:***** //Ask your service provider
Connection: GPRS //The 'connection - name'
Phone: Number //The dialup number to your service provider (Mine was *98*2#)
-> Details
Connection type: PPP
Idle timeout: //Time that lasts before the palm closes the connection if no activity.
Query DNS: //Not Checked if static DNS
Primary DNS: //The DNS from your service provider.
Secondary DNS: //The secondary DNS from your service provider.
IP Address: //Check automatic if dynamic IP
On the phone, I created a GPRS account, and then enabled the IrDA port...
Hope that could help a little.
Jens Peter