every R-18 is voiced.
from all ages: Kokuchou no Psychedelica and Haitaka no Psychedelica. Wand of fortune (vita port), variable barricade, NORN9,Ayakashi Gohan. and of course Karin games
...hmmm.. what else..
sorry, but I think not all of them. I've played some of R18 without voice :140:
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anyway, recently, I found out a VN made by a NanoReno participants which has the guy voiced, but not the heroine.
True, lots of the heroine doesn't have any voice, and that's probably not only because the amount of money they had to expend if all of the main characters need to be voiced, but also to help the reader imagine herself with her own voice as the heroine (just my opinion anyway)