I had to add to /etc/usb_modeswitch.d/1446:12d1:

# Huawei Mobile Broadband E1750
###############################

DefaultVendor=0x12d1
DefaultProduct=0x1446

TargetVendor = 0x12d1
TargetProduct= 0x1001
MessageContent="55534243000000000000000000000011060000000000000000000000000000" 
MessageEndpoint=0x01
CheckSuccess=5

Now modem is detected successfully, but it does not connect successfully.


Here's what I have on syslog:
May  6 18:17:53 lgl NetworkManager: <info>  Activation (ttyUSB0) starting connection 'Optimus'
May  6 18:17:53 lgl NetworkManager: <info>  (ttyUSB0): device state change: 3 -> 4 (reason 0)
May  6 18:17:53 lgl NetworkManager: <info>  Activation (ttyUSB0) Stage 1 of 5 (Device Prepare) scheduled...
May  6 18:17:53 lgl NetworkManager: <info>  Activation (ttyUSB0) Stage 1 of 5 (Device Prepare) started...
May  6 18:17:53 lgl NetworkManager: <info>  Activation (ttyUSB0) Stage 1 of 5 (Device Prepare) complete.
May  6 18:17:53 lgl NetworkManager: <WARN>  stage1_prepare_done(): GSM modem connection failed: (32) Sending command failed: device is connected
May  6 18:17:53 lgl NetworkManager: <info>  (ttyUSB0): device state change: 4 -> 9 (reason 1)
May  6 18:17:53 lgl NetworkManager: <info>  Marking connection 'Optimus' invalid.
May  6 18:17:53 lgl NetworkManager: <info>  Activation (ttyUSB0) failed.
May  6 18:17:53 lgl NetworkManager: <info>  (ttyUSB0): device state change: 9 -> 3 (reason 0)
May  6 18:17:53 lgl NetworkManager: <info>  (ttyUSB0): deactivating device (reason: 0).
May  6 18:17:53 lgl modem-manager: Modem /org/freedesktop/ModemManager/Modems/7: state changed (connected -> disconnecting)
May  6 18:17:53 lgl NetworkManager: <info>  (wlan0): writing resolv.conf to /sbin/resolvconf
May  6 18:17:53 lgl NetworkManager: <info>  Policy set 'FBWN' (wlan0) as default for routing and DNS.
May  6 18:17:54 lgl modem-manager: Modem /org/freedesktop/ModemManager/Modems/7: state changed (disconnecting -> registered)
May  6 18:18:17 lgl modem-manager: (ttyUSB0) closing serial device...
May  6 18:18:17 lgl kernel: [ 6631.157046] usb 1-3: USB disconnect, address 15
May  6 18:18:17 lgl kernel: [ 6631.157144] option: option_instat_callback: error -108
May  6 18:18:17 lgl kernel: [ 6631.157608] option1 ttyUSB0: GSM modem (1-port) converter now disconnected from ttyUSB0
May  6 18:18:17 lgl kernel: [ 6631.157640] option 1-3:1.0: device disconnected
May  6 18:18:17 lgl kernel: [ 6631.157946] option1 ttyUSB1: GSM modem (1-port) converter now disconnected from ttyUSB1
May  6 18:18:17 lgl kernel: [ 6631.157988] option 1-3:1.1: device disconnected
May  6 18:18:17 lgl kernel: [ 6631.158285] option1 ttyUSB2: GSM modem (1-port) converter now disconnected from ttyUSB2
May  6 18:18:17 lgl modem-manager: Modem /org/freedesktop/ModemManager/Modems/7: state changed (registered -> disabled)
May  6 18:18:17 lgl modem-manager: Removed modem /sys/devices/pci0000:00/0000:00:1d.7/usb1/1-3
May  6 18:18:17 lgl kernel: [ 6631.158324] option 1-3:1.2: device disconnected
May  6 18:18:17 lgl NetworkManager: <info>  (ttyUSB0): now unmanaged
May  6 18:18:17 lgl NetworkManager: <info>  (ttyUSB0): device state change: 3 -> 1 (reason 36)
May  6 18:18:17 lgl NetworkManager: <info>  (ttyUSB0): cleaning up...
May  6 18:18:17 lgl NetworkManager: <info>  (ttyUSB0): taking down device.
May  6 18:18:23 lgl kernel: [ 6637.388149] usb 1-3: new high speed USB device using ehci_hcd and address 16
May  6 18:18:23 lgl kernel: [ 6637.523897] usb 1-3: configuration #1 chosen from 1 choice
May  6 18:18:23 lgl kernel: [ 6637.526054] scsi56 : SCSI emulation for USB Mass Storage devices
May  6 18:18:23 lgl kernel: [ 6637.526502] usb-storage: device found at 16
May  6 18:18:23 lgl kernel: [ 6637.526506] usb-storage: waiting for device to settle before scanning
May  6 18:18:23 lgl kernel: [ 6637.526554] scsi57 : SCSI emulation for USB Mass Storage devices
May  6 18:18:23 lgl kernel: [ 6637.526836] usb-storage: device found at 16
May  6 18:18:23 lgl kernel: [ 6637.526840] usb-storage: waiting for device to settle before scanning
May  6 18:18:24 lgl usb-modeswitch: switching 12d1:1446 (HUAWEI Technology: HUAWEI Mobile)
May  6 18:18:24 lgl kernel: [ 6638.184113] usb 1-3: USB disconnect, address 16
May  6 18:18:28 lgl kernel: [ 6642.300115] usb 1-3: new high speed USB device using ehci_hcd and address 17
May  6 18:18:28 lgl kernel: [ 6642.434985] usb 1-3: configuration #1 chosen from 1 choice
May  6 18:18:28 lgl kernel: [ 6642.437262] option 1-3:1.0: GSM modem (1-port) converter detected
May  6 18:18:28 lgl kernel: [ 6642.437449] usb 1-3: GSM modem (1-port) converter now attached to ttyUSB0
May  6 18:18:28 lgl kernel: [ 6642.437718] option 1-3:1.1: GSM modem (1-port) converter detected
May  6 18:18:28 lgl kernel: [ 6642.437834] usb 1-3: GSM modem (1-port) converter now attached to ttyUSB1
May  6 18:18:28 lgl kernel: [ 6642.438074] option 1-3:1.2: GSM modem (1-port) converter detected
May  6 18:18:28 lgl kernel: [ 6642.438194] usb 1-3: GSM modem (1-port) converter now attached to ttyUSB2
May  6 18:18:28 lgl kernel: [ 6642.438786] scsi61 : SCSI emulation for USB Mass Storage devices
May  6 18:18:28 lgl kernel: [ 6642.438959] usb-storage: device found at 17
May  6 18:18:28 lgl kernel: [ 6642.438963] usb-storage: waiting for device to settle before scanning
May  6 18:18:28 lgl kernel: [ 6642.439405] scsi62 : SCSI emulation for USB Mass Storage devices
May  6 18:18:28 lgl kernel: [ 6642.439571] usb-storage: device found at 17
May  6 18:18:28 lgl kernel: [ 6642.439575] usb-storage: waiting for device to settle before scanning
May  6 18:18:28 lgl modem-manager: (Huawei): (ttyUSB1) deferring support check
May  6 18:18:28 lgl modem-manager: (Huawei): (ttyUSB2) deferring support check
May  6 18:18:28 lgl modem-manager: (ttyUSB0) opening serial device...
May  6 18:18:28 lgl modem-manager: (ttyUSB0): probe requested by plugin 'Huawei'
May  6 18:18:29 lgl usb-modeswitch: switched to 12d1:1001 (HUAWEI Technology: HUAWEI Mobile)
May  6 18:18:29 lgl modem-manager: (ttyUSB0) closing serial device...
May  6 18:18:29 lgl modem-manager: (Huawei): GSM modem /sys/devices/pci0000:00/0000:00:1d.7/usb1/1-3 claimed port ttyUSB0
May  6 18:18:29 lgl modem-manager: Added modem /sys/devices/pci0000:00/0000:00:1d.7/usb1/1-3
May  6 18:18:29 lgl modem-manager: Exported modem /sys/devices/pci0000:00/0000:00:1d.7/usb1/1-3 as /org/freedesktop/ModemManager/Modems/8
May  6 18:18:29 lgl NetworkManager: <info>  (ttyUSB0): new GSM device (driver: 'option1')
May  6 18:18:29 lgl NetworkManager: <info>  (ttyUSB0): exported as /org/freedesktop/NetworkManager/Devices/3
May  6 18:18:29 lgl NetworkManager: <info>  (ttyUSB0): now managed
May  6 18:18:29 lgl NetworkManager: <info>  (ttyUSB0): device state change: 1 -> 2 (reason 2)
May  6 18:18:29 lgl NetworkManager: <info>  (ttyUSB0): deactivating device (reason: 2).
May  6 18:18:29 lgl NetworkManager: <info>  (ttyUSB0): device state change: 2 -> 3 (reason 0)
May  6 18:18:31 lgl modem-manager: (ttyUSB1): re-checking support...
May  6 18:18:31 lgl modem-manager: (ttyUSB1) opening serial device...
May  6 18:18:31 lgl modem-manager: (ttyUSB2): re-checking support...
May  6 18:18:31 lgl modem-manager: (ttyUSB2) opening serial device...
May  6 18:18:31 lgl modem-manager: (ttyUSB2) closing serial device...
May  6 18:18:31 lgl modem-manager: (Huawei): GSM modem /sys/devices/pci0000:00/0000:00:1d.7/usb1/1-3 claimed port ttyUSB2
May  6 18:18:33 lgl kernel: [ 6647.437390] usb-storage: device scan complete
May  6 18:18:33 lgl kernel: [ 6647.437425] usb-storage: device scan complete
May  6 18:18:33 lgl kernel: [ 6647.438868] scsi 61:0:0:0: CD-ROM            HUAWEI   Mass Storage     2.31 PQ: 0 ANSI: 2
May  6 18:18:33 lgl kernel: [ 6647.439195] scsi 62:0:0:0: Direct-Access     HUAWEI   SD Storage       2.31 PQ: 0 ANSI: 2
May  6 18:18:33 lgl kernel: [ 6647.452496] sr1: scsi-1 drive
May  6 18:18:33 lgl kernel: [ 6647.453654] sr 61:0:0:0: Attached scsi CD-ROM sr1
May  6 18:18:33 lgl kernel: [ 6647.457352] sr 61:0:0:0: Attached scsi generic sg2 type 5
May  6 18:18:33 lgl kernel: [ 6647.460681] sd 62:0:0:0: Attached scsi generic sg3 type 0
May  6 18:18:33 lgl kernel: [ 6647.466390] sd 62:0:0:0: [sdb] Attached SCSI removable disk
May  6 18:18:36 lgl modem-manager: (ttyUSB1) closing serial device...
May  6 18:18:36 lgl modem-manager: (ttyUSB1) opening serial device...
May  6 18:18:36 lgl modem-manager: (ttyUSB1): probe requested by plugin 'Generic'
May  6 18:18:45 lgl NetworkManager: <info>  Activation (ttyUSB0) starting connection 'Optimus'
May  6 18:18:45 lgl NetworkManager: <info>  (ttyUSB0): device state change: 3 -> 4 (reason 0)
May  6 18:18:45 lgl NetworkManager: <info>  Activation (ttyUSB0) Stage 1 of 5 (Device Prepare) scheduled...
May  6 18:18:45 lgl NetworkManager: <info>  Activation (ttyUSB0) Stage 1 of 5 (Device Prepare) started...
May  6 18:18:45 lgl NetworkManager: <info>  Activation (ttyUSB0) Stage 1 of 5 (Device Prepare) complete.
May  6 18:18:45 lgl modem-manager: (ttyUSB0) opening serial device...
May  6 18:18:45 lgl modem-manager: Modem /org/freedesktop/ModemManager/Modems/8: state changed (disabled -> enabling)
May  6 18:18:46 lgl modem-manager: Modem /org/freedesktop/ModemManager/Modems/8: state changed (enabling -> enabled)
May  6 18:18:46 lgl modem-manager: Registration state changed: 2
May  6 18:18:46 lgl modem-manager: Modem /org/freedesktop/ModemManager/Modems/8: state changed (enabled -> searching)
May  6 18:18:49 lgl modem-manager: (ttyUSB1) closing serial device...
May  6 18:18:53 lgl modem-manager: Registration state changed: 1
May  6 18:18:53 lgl modem-manager: Modem /org/freedesktop/ModemManager/Modems/8: state changed (searching -> registered)
May  6 18:18:53 lgl modem-manager: Modem /org/freedesktop/ModemManager/Modems/8: state changed (registered -> connecting)
May  6 18:18:53 lgl modem-manager: Modem /org/freedesktop/ModemManager/Modems/8: state changed (connecting -> connected)
May  6 18:18:53 lgl NetworkManager: <info>  Activation (ttyUSB0) Stage 2 of 5 (Device Configure) scheduled...
May  6 18:18:53 lgl NetworkManager: <info>  Activation (ttyUSB0) Stage 2 of 5 (Device Configure) starting...
May  6 18:18:53 lgl NetworkManager: <info>  (ttyUSB0): device state change: 4 -> 5 (reason 0)
May  6 18:18:53 lgl NetworkManager: <info>  Activation (ttyUSB0) Stage 2 of 5 (Device Configure) successful.
May  6 18:18:53 lgl NetworkManager: <info>  Activation (ttyUSB0) Stage 3 of 5 (IP Configure Start) scheduled.
May  6 18:18:53 lgl NetworkManager: <info>  Activation (ttyUSB0) Stage 2 of 5 (Device Configure) complete.
May  6 18:18:53 lgl NetworkManager: <info>  Activation (ttyUSB0) Stage 3 of 5 (IP Configure Start) started...
May  6 18:18:53 lgl NetworkManager: <info>  (ttyUSB0): device state change: 5 -> 7 (reason 0)
May  6 18:18:53 lgl NetworkManager: <info>  Starting pppd connection
May  6 18:18:53 lgl NetworkManager: <debug> [1273166333.181642] nm_ppp_manager_start(): Command line: /usr/sbin/pppd nodetach lock nodefaultroute ttyUSB0 noipdefault noauth usepeerdns lcp-echo-failure 5 lcp-echo-interval 30 ipparam /org/freedesktop/NetworkManager/PPP/0 plugin /usr/lib/pppd/2.4.4/nm-pppd-plugin.so
May  6 18:18:53 lgl NetworkManager: <debug> [1273166333.184911] nm_ppp_manager_start(): ppp started with pid 5763
May  6 18:18:53 lgl NetworkManager: <info>  Activation (ttyUSB0) Stage 4 of 5 (IP6 Configure Get) scheduled...
May  6 18:18:53 lgl NetworkManager: <info>  Activation (ttyUSB0) Stage 3 of 5 (IP Configure Start) complete.
May  6 18:18:53 lgl NetworkManager: <info>  Activation (ttyUSB0) Stage 4 of 5 (IP6 Configure Get) started...
May  6 18:18:53 lgl NetworkManager: <info>  Activation (ttyUSB0) Stage 4 of 5 (IP6 Configure Get) complete.
May  6 18:18:53 lgl pppd[5763]: Plugin /usr/lib/pppd/2.4.4/nm-pppd-plugin.so loaded.
May  6 18:18:53 lgl pppd[5763]: pppd 2.4.5 started by root, uid 0
May  6 18:18:53 lgl NetworkManager:    SCPlugin-Ifupdown: devices added (path: /sys/devices/virtual/net/ppp0, iface: ppp0)
May  6 18:18:53 lgl NetworkManager:    SCPlugin-Ifupdown: device added (path: /sys/devices/virtual/net/ppp0, iface: ppp0): no ifupdown configuration found.
May  6 18:18:53 lgl pppd[5763]: Using interface ppp0
May  6 18:18:53 lgl pppd[5763]: Connect: ppp0 <--> /dev/ttyUSB0
May  6 18:18:53 lgl pppd[5763]: CHAP authentication succeeded
May  6 18:18:53 lgl pppd[5763]: CHAP authentication succeeded
May  6 18:18:59 lgl pppd[5763]: Modem hangup
May  6 18:18:59 lgl pppd[5763]: Connection terminated.
May  6 18:18:59 lgl NetworkManager: <info>  (ttyUSB0): device state change: 7 -> 9 (reason 13)
May  6 18:18:59 lgl NetworkManager: <info>  Marking connection 'Optimus' invalid.
May  6 18:18:59 lgl NetworkManager: <info>  Activation (ttyUSB0) failed.
May  6 18:18:59 lgl NetworkManager: <info>  (ttyUSB0): device state change: 9 -> 3 (reason 0)
May  6 18:18:59 lgl NetworkManager: <info>  (ttyUSB0): deactivating device (reason: 0).
May  6 18:18:59 lgl modem-manager: (ttyUSB0) closing serial device...
May  6 18:18:59 lgl modem-manager: Modem /org/freedesktop/ModemManager/Modems/8: state changed (connected -> disconnecting)
May  6 18:18:59 lgl modem-manager: Modem /org/freedesktop/ModemManager/Modems/8: state changed (disconnecting -> connected)
May  6 18:18:59 lgl NetworkManager: <info>  (wlan0): writing resolv.conf to /sbin/resolvconf
May  6 18:18:59 lgl NetworkManager: <info>  Policy set 'FBWN' (wlan0) as default for routing and DNS.
May  6 18:18:59 lgl NetworkManager:    SCPlugin-Ifupdown: devices removed (path: /sys/devices/virtual/net/ppp0, iface: ppp0)
May  6 18:19:00 lgl pppd[5763]: Exit.
May  6 18:19:02 lgl NetworkManager: <debug> [1273166342.001263] ensure_killed(): waiting for ppp pid 5763 to exit
May  6 18:19:02 lgl NetworkManager: <debug> [1273166342.001441] ensure_killed(): ppp pid 5763 cleaned up

Sometimes NM even crashes.