Recently i had written the post about Huawei D100 O2 Surf Station (Germany). Huawei D100T wifi router gateway is different than other USB modems and routers. Huawei D100T router gateway needs USB modem to use it.

Like another WiFi Routers, Gateway and Modems Huawei D100T can also be unlocked. But, unlocking of Huawei this Router Gateway is different than the Huawei USB modems and routers. Huawei D100T Router Gateway can not be unlocked with card lock unlock tool or Huawei modem code writer tool, because Huawei D100T Router Gateway has no USB port. Huawei D100T Router Gateway comes with LAN ports. But, Huawei D100T Router Gateway can be unlocked with FMC unlocker tool. FMC Unlocker tool / Software can be downloaded from the download link which is provided at the end of the article.
To unlock your D100T Huawei WiFi Router Gateway, connect via RJ45 cable to PC and close all the running software. Now run FMC unlocker software and detect your device under that. Now when D100T imei will be visible in FMC unlocker software then put unlock code of WiFi Router and click on unlock and you have successfully unlocked your D100T Huawei WiFi Router Gateway. Now dance around the room and use any another network provider sim on it.
Update: Refer this guide to unlock Huawei D100/D100T routers.