i used to use 12.04 LTS and had the same problem..upgraded to 12.10 as i have read somewhere that 12.10 has a fix for it...but i still face the same problem..
*i have wvdial...usb-mode switch packages
*my modem also shows up in lsusb command
*i have added my modem under the mobile broadband tab of network settings
*enabled networking in recovery mode
NOTE:-when i boot up in the recovery mode..the option is available in the network settings to "ENABLE BROADBAND" and also my modem shows up and i am able to connect it...but i am unable to do so in the normal boot.
p.s:- i use tata photon +