In order to support X.25 DTE-DTE over the B-channel, you need a modem which supports CAPI 2 and ISO 8208.
The only ISDN modems we have found that reliably support ISO 8208 are the BT Speedway and the Eicon Diva series. We normally recommend the Eicon Diva Pro or the Speedway.
The following ISDN devices have been tested with ODEX but do not have the required CAPI support (we will continue to update this list):
- Microcom ISDN Porte2 card
- ELSA MicroLink ISDN USB
- Zyxel ISDN TA Omninet Plus
- Hayes Acura