When I connect my Treo 650 with a USB cable it works
sometimes and not others. A little investigation showed
that it always works when I see the Palm device listed
in the output of lsusb. While trying to diagnose why
it appears sometimes and not others, I discovered that
it sometimes appears in /proc/bus/usb/devices and not
in lsusb. I didn't think that was possible!

I've tried running kudzu (the Red Hat hardware discovery
tool) and killing and restarting udevd. No joy.

Any advice for further troubleshooting?

Greetingz!

Well, in order for your Treo 650 to work via USB (or anything, for that matter), it will *always* have to be recognized by your Linux system.

When the device shows up in the output from "lsusb", that's great, and exactly what you want. However, when it doesn't show up, I would do the following;
1) Make sure you have a good USB cable (I had that exact phone and the cable that came with it was a total flake)
2) Check the output from the "dmesg" command, see if a module (aka "Driver") crashed when it saw the device and started to initialize.

There could also be another problem; which port are you (always) plugging the device in? I've seen a few laptops & desktops that had the inside "tab" if their most-used USB port snap right off.

Good luck!

P.S: Apologies for the *really* late reply! Happy 1 year anniversary!

Thanks for the response. I bought a new phone long ago and forgot
about this post. Now that you mention the cable, that would be the
prime suspect. That's the one piece of the puzzle I didn't thoroughly
test.