USM (USB Mass Storage) was replaced by MTP somewhere with, at latest, ICS. Some kernels still may contain for USM, but most won't anymore. So here are your options:
- Check the market for Apps which can enable USM again (I heard mentioned a few who should be able doing so, including AL Mass Storage Manager, USB Mass Storage Watcher, and Usb Host Controller -- but no guarantees whatsoever, as I didn't try any due to lack of ICS devices
- install the mtp packages on Ubuntu (
apt-get install mtp-tools)