My original program, PdaNet, only works on Windows variants, so I'm trying a different program called, in a most original fashion, USB Modem.
I've tried several methods, including their command-line script, gnome-ppp (which doesn't quite work with Ubuntu 7.10 right now), and kppp. In each case, I've gotten as far as getting an IP address and DNS information, which, as far as I'm concerned, is a damn good indicator of a functioning connection.
Except I still can't move any data. The most positive indicator I've had is that in the case of a local, active WiFi connection, making the Treo connection stops all data dead. So at least it, y'know, mucks with the WiFi.
Adding to the confusion is that sometime around my last attempt with kppp, I apparently lost the ability to get onto the network from the Treo itself. It says it connects perfectly well, but no data goes through. Something that doesn't change even with a hard reset.
So I don't know if I've somehow messed up the Treo (doubtful), AT&T has cut me off, or they've just lost local net connectivity (which has happened a time or two).