'BIG' UPDATE I reinstalled the package (as I and binW pointed out) and now it recognises the modem as a modem. I configured the network, but I can't connect (acording to the 'lights' the modem shows I need to introduce the modem), so if you could help me with this last step i'll mention you in a comment on the source code of my next programm ;)
When I connect my usb modem to the computer it appears as a 'normal' usb, that is, it doesn't recognise it is a usb modem, so I can't connect my computer to the internet.
Is there any way to solve this? I already have installed usb-modeswitch, if that helps you :)
EDIT: the syslog ->
[ 899.168328] usb 2-4: USB disconnect, address 4
[ 899.219995] scsi 10:0:0:0: rejecting I/O to dead device
[ 907.436065] usb 2-4: new high speed USB device using ehci_hcd and address 5
[ 907.570709] usb 2-4: configuration #1 chosen from 1 choice
[ 907.572502] scsi12 : SCSI emulation for USB Mass Storage devices
[ 907.572849] usb-storage: device found at 5
[ 907.572852] usb-storage: waiting for device to settle before scanning
[ 907.572896] scsi13 : SCSI emulation for USB Mass Storage devices
[ 907.573116] usb-storage: device found at 5
[ 907.573118] usb-storage: waiting for device to settle before scanning
[ 912.572899] usb-storage: device scan complete
[ 912.573352] usb-storage: device scan complete
[ 912.573607] scsi 12:0:0:0: CD-ROM HUAWEI Mass Storage 2.31 PQ: 0 ANSI: 2
[ 912.573974] scsi 13:0:0:0: Direct-Access HUAWEI SD Storage 2.31 PQ: 0 ANSI: 2
[ 912.580691] sr1: scsi-1 drive
[ 912.580880] sr 12:0:0:0: Attached scsi CD-ROM sr1
[ 912.580989] sr 12:0:0:0: Attached scsi generic sg3 type 5
[ 912.581309] sd 13:0:0:0: Attached scsi generic sg4 type 0
[ 912.594637] sd 13:0:0:0: [sdc] Attached SCSI removable disk
[ 925.115931] ISO 9660 Extensions: Microsoft Joliet Level 1
[ 925.116685] ISOFS: changing to secondary root
EDIT 2 Just in case it is relevant, it used to work out of the box on ubuntu 11.04, but not on 10.04 (my case) (I can't upgrade, don't ask me to do that, please)
EDIT 3 i've been doing some research and it seems it should work perfectly with usb-modeswitch, so I'll try to reinstall it.