Modems are often bought from mobile operators and maybe have lock to prevent using SIM cards from other operators.
If you do not plan to use SIM cards from other operators, skip this section.
You have different ways to unlock:
AT^CARDLOCK=“< code >”command
Unlock tools: Huawei unlock
The main source of firmware files are in dc-files. You can browse for your model and download firmware update (normally zip containing .exe file). For update, need windows computer (xp, vista or w7). The process is very straightforward, only execute exe file and follow indications.
Some models need unlock code to flash firmware. You can use unlock huawei tools for that.
After upgrade process, run dc-unlocker client to check if voice is enabled.
There is a lot of different models from Huawei vendor. Primarly, they are used for data connection to internet, but some of them are voice capable. This means, that you can make calls with the right software. Some telcos include this piece of software, but, in any case, you can use Mobile Partner for that purpose in Windows systems. Only need to upgrade firmware and install tool.
To know if your dongle supports voice, you can use two methods:
Models k3520, e169, k3765 and k3715 have voice enabled if you upgrade firmware. E1750 needs dc-unlocker voice activation.