What types of companies are using conference calling today?

Question

I would like to know what types of companies are using reservationless calling these days? Are companies using GoToMyPC for web conference calling, today with so many options is there a market for reservationless calling at a low rate (Lower than AT&T etc) ?
Any feedback or personal experience with conference calling would be appreciated....i.e. what type of company you work for and if it is a service you use...Basically I dont want to be ripped off when you can conference differently thanksss