Carrier limits the voice funciton? about MC8785v and MC8775v

[onescoop]

Many people wonder why there is no voice even they used the voice capacity unlocked Sierra Wireless embedded module WWAN cards, such as MC8785v and MC8775v.

I heard from a friend that he tried and found:

MC8785v+X300 with CMCC(China Mobile Communication Cooperation) SIM card and make calls in China, no voice.

MC8785v+X300 with AT&T SIM card make calls in USA, there is voice!

So, it might be the carrier limits the voice function for embedded WWAN cards?

Then if anyone can try different carriers in different countries, pls try it for us