I know this is a rather irrelevant info for most of the users when Maxx 5G SA is the talk of the town. Nevertheless, FYI. I was casually trying out Simba Voice and bingo, it prompts for OTP, quickly, I swapped my SIM card to the other old VoLTE device which is SIMBA VoLTE incompatible, it managed to register Voice app successfully. I don't know when SIMBA re-enables it again but thankfully, my old Android devices are 1/2 relevant (being only can call out and not call in if app not on screen) again. 
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