The Chinese Xiaomi website explicitly mentions full netcom 3.0 which supports concurrent 4G/3G-voice, after the section on HD Voice.
http://www.mi.com/mi5/features
全网通 3.0 提升双卡信号质量
在全网通 3.0 时代到来前,每每进入网络覆盖不佳的区域时,主卡的通话质量尚且稳定清晰,副卡的表现却往往不尽人意。新的全网通 3.0 改变这一现状,当主卡支持移动、联通 4G 网络,副卡突破性的支持联通 3G 网络语音通话,双卡双待的通话信号质量因此有了更好的表现。
However, the Indian website doesn't mention concurrent 4G/3G-voice at all at
http://www.mi.com/in/mi5/tech even though that particular page is clearly meant to be an equivalent version of the Chinese webpage.
Furthermore, it looks like the Chinese and Indian models support slightly different network bands. The Indian model drops CDMA support in exchange for FDD-LTE B5 band.
Chinese:
FDD-LTE (频段 B1,B3,B7)
TD-LTE (频段 B38,B39,B40,B41)
TD-SCDMA (频段 B34,B39)
WCDMA (频段 B1,B2,B5,B8)
GSM (频段 B2,B3,B5,B8)
CDMA1X/EVDO (频段 BC0)
Indian:
FDD-LTE: B1 / B3 / B5 / B7
TD-LTE: B38 / B39 / B40 / B41
TD-SCDMA: 1900 / 2000MHz
WCDMA: 850 / 900 / 1900 / 2100MHz
GSM: 850 / 900 / 1800 / 1900MHz
So we know hardware-wise, the Chinese and Indian models are different. I'm wondering if the international model of the Mi5 (assuming it's the same as the Indian one) will also allow concurrent 4G/3G-voice, or if it's only specific to the Chinese model?
If only the Chinese model supports concurrent 4G/3G-voice, this then raises the question of whether the global ROM itself will support this feature, or would we have to stick with the Chinese ROM and all its problems like missing Playstore?