Some times, the device will only detect it as a USB cd-rom.Once dmesg
confirms /dev/ttyUSB0.. etc, then you are on the way.
otherwise use http://www.draisberghof.de/usb_modeswitch/
one more tool also cab be used for USB data card: saks3g(
http://wiki.darknet.co.za/pmwiki.php/Posts/Sakis3gUsbModem)