A: No. The B312-926 hardware does not support VoLTE, only CSFB.
AT^SYSCFGEX="00",3FFFFFFF,1,2,7FFFFFFFFFFFFFFF,, This enables all bands and aggressive CA scanning. Create a cron job via telnet (install dropbear first): huawei b312926 firmware 10031h192sp9c00 universal repack
MD5 checksum for genuine 10031H192SP9C00_Universal_Repack.bin (example – verify with your source): only CSFB. AT^SYSCFGEX="00"