Hi,
Also bought my black Lumia 920 from Vietnam and I?m having massive problems getting the LTE work here in Finland where I live.
I?ve tried about 5 different software/firmware versions of which every one has worked but not the LTE. No other options in
settings-mobile network-highest connection speed than 2G only and 3G only.
I?m starting to suspect that the Lumia they sell in Vietnam actually has no LTE support at all.. Trying out the newer 1308 firmwares at this very moment.
Good luck and let me know if you get yours to work