This is a low cost 3G Dongle, often found O2 branded. It supports GSM voice calls and can work with Asterisk and other PBX softwares. Tools such as DC Unlocker and, indeed, interrogating the dongle directly with a terminal programme may claim voice is enabled but you will get no audio when you make voice calls and/or Asterisk says “AT^DDSETEX failed”.
You need to flash the firmware of the dongle to 11.609.10.02.432. This used to be hosted on quite a few sites, but it’s incredibly difficult to find now. I’ve tracked down the installer and hosted a copy on my blog. You can download the firmware here.
In my case, as soon as the firmware was upgraded, voice worked correctly and Asterisk no longer said “AT^DDSETEX failed”.