$  ls -l /dev/ttyACM0 
crw-rw---- 1 root dialout 166, 0 2011-01-19 17:52 /dev/ttyACM0

# lsusb -t
...
    |__ Port 3: Dev 5, If 0, Class=comm., Driver=cdc_acm, 480M
    |__ Port 3: Dev 5, If 1, Class=data, Driver=cdc_acm, 480M
...

And from syslog:

Jan 19 17:52:33 localhost kernel: [  852.680190] usb 1-3: new high speed USB device using ehci_hcd and address 4
Jan 19 17:52:33 localhost udevd-work[4695]: error opening ATTR{/sys/devices/pci0000:00/0000:00:1a.7/usb1/1-3/idProduct} for writing: Permission denied
Jan 19 17:52:33 localhost kernel: [  853.191275] usb 1-3: usbfs: process 4698 (usb_modeswitch) did not claim interface 0 before use
Jan 19 17:52:33 localhost kernel: [  853.194161] usb 1-3: USB disconnect, address 4
Jan 19 17:52:35 localhost kernel: [  854.580170] usb 1-3: new high speed USB device using ehci_hcd and address 5
Jan 19 17:52:35 localhost kernel: [  855.243560] usb 1-3: selecting invalid altsetting 1
Jan 19 17:52:35 localhost kernel: [  855.243580] usbcore: registered new interface driver uas
Jan 19 17:52:35 localhost udevd-work[4695]: error opening ATTR{/sys/devices/pci0000:00/0000:00:1a.7/usb1/1-3/idProduct} for writing: Permission denied
Jan 19 17:52:35 localhost udevd-work[4700]: error opening ATTR{/sys/devices/pci0000:00/0000:00:1a.7/usb1/1-3/idProduct} for writing: Permission denied
Jan 19 17:52:35 localhost kernel: [  855.252717] Initializing USB Mass Storage driver...
Jan 19 17:52:35 localhost kernel: [  855.252860] scsi5 : usb-storage 1-3:1.5
Jan 19 17:52:35 localhost kernel: [  855.253599] usbcore: registered new interface driver usb-storage
Jan 19 17:52:35 localhost kernel: [  855.253602] USB Mass Storage support registered.
Jan 19 17:52:35 localhost kernel: [  855.279948] cdc_acm 1-3:1.0: ttyACM0: USB ACM device
Jan 19 17:52:35 localhost kernel: [  855.292394] usbcore: registered new interface driver cdc_acm
Jan 19 17:52:35 localhost kernel: [  855.292396] cdc_acm: v0.26:USB Abstract Control Model driver for USB modems and ISDN adapters
Jan 19 17:52:35 localhost modem-manager: (ttyACM0) opening serial port...
Jan 19 17:52:35 localhost modem-manager: (ttyACM0): probe requested by plugin 'Generic'
Jan 19 17:52:36 localhost kernel: [  856.254450] scsi 5:0:0:0: CD-ROM            UMW190   CD-ROM           2.31 PQ: 0 ANSI: 2
Jan 19 17:52:36 localhost kernel: [  856.259527] sr1: scsi3-mmc drive: 24x/24x xa/form2 caddy
Jan 19 17:52:36 localhost kernel: [  856.260493] sr 5:0:0:0: Attached scsi CD-ROM sr1
Jan 19 17:52:36 localhost kernel: [  856.262242] sr 5:0:0:0: Attached scsi generic sg2 type 5
Jan 19 17:52:37 localhost modem-manager: (ttyACM0) closing serial port...
Jan 19 17:52:37 localhost modem-manager: (ttyACM0) opening serial port...
Jan 19 17:52:37 localhost modem-manager: (Generic): CDMA modem /sys/devices/pci0000:00/0000:00:1a.7/usb1/1-3 claimed port ttyACM0
Jan 19 17:52:37 localhost modem-manager: Added modem /sys/devices/pci0000:00/0000:00:1a.7/usb1/1-3
Jan 19 17:52:37 localhost modem-manager: (tty/ttyACM0): outstanding support task prevents export of /sys/devices/pci0000:00/0000:00:1a.7/usb1/1-3
Jan 19 17:52:38 localhost modem-manager: (ttyACM0) closing serial port...
Jan 19 17:52:38 localhost modem-manager: Exported modem /sys/devices/pci0000:00/0000:00:1a.7/usb1/1-3 as /org/freedesktop/ModemManager/Modems/0
Jan 19 17:52:38 localhost modem-manager: (/org/freedesktop/ModemManager/Modems/0): data port is ttyACM0
Jan 19 17:52:38 localhost NetworkManager[838]: <warn> (ttyACM0): failed to look up interface index
Jan 19 17:52:38 localhost NetworkManager[838]: <info> WWAN now disabled by radio killswitch
Jan 19 17:52:38 localhost NetworkManager[838]: <info> (ttyACM0): new CDMA device (driver: 'cdc_acm' ifindex: -1)
Jan 19 17:52:38 localhost NetworkManager[838]: <info> (ttyACM0): exported as /org/freedesktop/NetworkManager/Devices/2
Jan 19 17:52:38 localhost NetworkManager[838]: <info> (ttyACM0): now managed
Jan 19 17:52:38 localhost NetworkManager[838]: <info> (ttyACM0): device state change: 1 -> 2 (reason 2)
Jan 19 17:52:38 localhost NetworkManager[838]: <info> (ttyACM0): deactivating device (reason: 2).
Jan 19 17:52:38 localhost NetworkManager[838]: <info> (ttyACM0): device state change: 2 -> 3 (reason 0)