Our Company have never used voice chat. I lead our raids each week and I trust my members to know their roles in each encounter. We're attempting Twintania tomorrow night and I will be doing the same thing I have done in all previous Turns;

I ask our members to do some of their own research before hand on Reddit, YouTube or the Forums; and spend some time doing written instructions to place in a party chat macro, both to save time during the run and so that I don't miss anything out.

It might be easier having people talk on chat, but then again this is the way we've learned and this is what we are comfortable with. A couple of people were shocked that we cleared Turn 4 our first night in there, without the use of voice chat. I think all you need are good instructions and reliable members; if you're having to shout at someone to do something mid run, something is wrong.