The only place I've had an issue is within the parks themselves. They've expanded wifi throughout the property, and it works pretty well in the hotels.

It is free, and there is no option to pay for premium.

I can tell you that I did not have any problems at all over the last few years. However, I'm not doing video conferences. During the day you shouldn't run into many problems unless everyone at your conference is also doing video in the middle of the day.