"DC-Unlocker2 client" is a program that is capable of unlocking SIM-locked USB modems, phones, and routers, so you can use them with any network operator worldwide. It comes along with a hardware part called DC-Unlocker dongle. The hardware is used for managing phones and modems that cannot be unlocked via their IMEI numbers.
Other devices that can be unlocked just by their IMEI # don't require the hardware part of the package and can be unlocked remotely.
The program supports many of the most famous phone and modem models from Huawei, Vodafone, ZTE, Novatel, and others. It has the ability to automatically identify your connected device, but you can also choose it manually. A detailed debug screen will show you everything about your device and the processes being done. The program is also capable of working with the device software - this is called flashing.
If you buy the DC-Unlocker dongle, these unlocking services will require less credits and many modems will even be unlocked for free. But if you do not, then you will have to purchase credits, whose required amount will vary depending on the brand of the datacard or phone.