We have a new Motorola Razr V9m Bronze cellphone which is invisible when connected to Kubuntu computers as a USB drive. It works fine on Windows machines, and it works on at least one Debian system. But on Kubuntu Fiesty and Hardy, the phone detects the connection but the computer does not. Nothing appears in dmesg or lsusb output.

The Debian system which works is running kernel version 2.6.23. One of the two tested Kubuntu systems is running 2.6.20, the other is running 2.6.24. So the problem didn't start or end with a particular kernel version.

Is there any way to diagnose the problem on the affected machines?
Are there any known USB issues which might cause this problem?

Open up a terminal before connecting the device. Enter "sudo tail -f /var/log/messages". Is the device noticed at all? Does auto-mounting of normal pendrives work? My guess is that you need to search on google for "udev" and "Motorola Razr" and see if you can find udev rules for this device.