Unlocking a Huawei D100 requires the original firmware from the network removed to a generic firmware.

You can download the generic firmware

Rebranded
O2 Surf Station (Germany)
3WLAN Adapter D100 (Austria)
T-Mobile Share Dock (UK)
Wind (Italy)

To unlock the Huawei D100/D100T follow these video instructions:

https://www.youtube.com/watch?v=Tc5t8qJlZf0

Download D100 Firmware Update
Download an update from above and extract it to your computer:Before flashing make sure your computer and the Huawei D100 won’t lose power during the process as it could potentially brick your Huawei D100!

Power on the Huawei D100 and connect it to computer through an Ethernet cable
Launch FmcUpdate.exe from the extracted files
Click the “Check” button to detect your Huawei D100 and shift it to update mode
Click the “Upgrade” button to start the update
Wait a couple minutes until the whole progress is accomplished
After upgrade, disconnect the Ethernet cable and push the reset button of the Huawei D100 (in the lower right corner of the backside) or restore factory defaults in the webinterface (open http://192.168.1.1 in your browser and enter “admin” as default password, then go to Advanced Settings | System | Restore Defaults | Restore).
note: If you do not restore to factory defaults after the update, your USB modem won’t be detected properly and the “Connection” page will say “The USB Modem is nonexistent”
Connect your USB modem to the Huawei D100 port only when it’s switched off!
Turn-on the router and go to the GUI by opening http://192.168.1.1 in your browser and enter “admin” as password.
To activate an access profile for your network operator, go to Advanced Settings | Dial Up Settings | Profile Settings and chose your provider from the Profile List. If your provider’s settings are not included, just create a new profile by entering a Profile Name and all the other information required below and click on Save.
Afterwards go to Advanced Settings | Dial Up Settings | PPP Settings and make sure the correct profile is chosen in the Profile List. If not, chose the correct one and hit Apply.
Now your router is ready to share your broadband (remember that your USB modem must also be unlocked!).
You might want to enable (really) secure WiFi-encryption under Advanced Settings | WLAN Settings | WLAN Advance Settings where you should set WPA-PSK|WPA2-PSK as Encryption Mode and TKIP+AES as WPA Encryption. Lastly enter the WPA Pre-Shared Key, which should be not too easy to guess and hit Apply.

D100 supported USB-modems
Huawei E156, E156G
Huawei E160, E160G, E160E, E160X, K3565(-H)
Huawei E169, E169G, E169V, K3520
Huawei E170
Huawei E172
Huawei E176 / T-Mobile web’n’walk Stick IV
Huawei E1762 / BILDmobil Speedstick
Huawei E220
Huawei E270
Huawei E272
Huawei K3715
Huawei E1750
Huawei E122
Huawei E1550
Huawei E180
presumably all other recent Huawei USB-modems
Access Point Name (APN) settings for UK mobile network providers.

Whichever mobile network you use, try setting the APN to ‘Dynamic’ initially and use the appropriate username \ password below. If it doesn’t work change to ‘Static’ and manually enter the APN setting.

All settings are case sensitive!

The number to dial is normally *99#

Vodafone
APN (contract): internet
APN (PAYG): pp.vodafone.co.uk
Username: web
Password: web
Orange
APN: orangeinternetUsername: leave blank
Password: leave blank
O2
APN (contract): mobile.o2.co.uk
APN (PAYG): m-bb.o2.co.uk
Username: web
Password: web
T-Mobile
APN: general.t-mobile.uk
Username: leave blank
Password: leave blank
Three
APN:3internetUsername: leave blankPassword:leave blank
Tesco Mobile (uses the O2 network)
APN: prepay.tesco-mobile.com
Username: tescowap
Password: password
Virgin Mobile (uses the T-Mobile network)
APN: goto.virginmobile.uk
Username: user
Password: leave blank
BT Mobile (uses the Vodafone network)
APN: btmobile2.bt.com
Username: bt
Password: bt
ASDA Mobile (uses the Vodafone network)
APN: asdamobiles.co.uk
Username: web
Password: web
Manx Telecom (Isle of Man)
APN: 3gpronto
Username: leave blank
Password: leave blank
Sure Mobile (Guernsey & Isle of Man)
APN: internet
Username: leave blank
Password: leave blank
Wave Telecom (Guernsey)APN: pepper
Username: leave blank
Password: leave blank
Airtel Vodafone (Guernsey)
APN: airtel-ci-gprs.com
Username: leave blank
Password: leave blank
Sure Mobile (Jersey)
APN: internet
Username: leave blank
Password: leave blank
Jersey Telecom(Jersey)
APN: pepper
Username: leave blank
Password: leave blank
Airtel Vodafone (Jersey)
APN: airtel-ci-gprs.com
Username: leave blank
Password: leave blank