Worked this out with Anders last night. Thank you Anders, awesome hands-on support for ThermIQ indeed!
Cdc-acm and usbserial kernel modules both support the same device and since cdc-acm runs first and creates ttyACM0, usbserial is not able to create ttyUSB0.
The fix sequence goes something like this:
1. Blacklist the cdc-acm kernel module by adding the following line to /etc/modprobe.d/blacklist:
blacklist cdc-acm
2. rmmod cdc_acm (not sure if really needed)
3. modprobe usbserial vendor=0x4d8 product=0xfdeb
(also add to /etc/modules:
usbserial vendor=0x04d8 product=0xfdeb)
4. Unplug the usb and plug it again.
5. chmod 0666 /dev/ttyUSB0
(add this to some startup script)
-Tapani