Huawei E1750 3G Modem has the ability to call, but the feature is disabled by default.
Most online solutions on enabling the voice feature do not work, including manual AT commands, the cracked version of dc unlocker or huawei unlocker.
I am not sure what the actual dc unlocker voice activation (4 credits) does, but it successfully activated the voice feature.
This video is just me trying out the dc unlocker voice activation (with credits T_T) in a virtual machine.
After this, the raspbx chan_dongle works 😀
Damage: 4 credits
Video Tutorial and Walkthrough