I have the Option GT Max card (express 34 not USB) on AT&T. I stopped using the vendor software under Leopard and simply selected my card and entered my information in the Network preferences panel. This actually works very well and continues to work under Snow Leopard.
I use the following settings:
isp.cingular for the account name.
leave the password field blank.
Option N.V. as the vendor on the Advanced tab, WWAN sub tab.
GSM as the Model on the Advanced tab, WWAN sub tab.
ISP.CINGULAR as the APN on the Advanced tab, WWAN sub tab.
1 as the CID on the Advanced tab, WWAN sub tab.
For whatever reason, these settings changed to the following when I installed Snow Leopard but I can still connect.
Apple as the vendor on the Advanced tab, WWAN sub tab.
Apple modem (v.32) as the Model on the Advanced tab, WWAN sub tab.
You may try this if you haven't already. Good luck