6 hours. A friend of mine from Australia had a block price for stateside calls. 3 hours for a flatrate. We talked the 3 hours hung up and then she called me right back and we talked for 3 more hours.
I once dialed a porn phone number to talk to a lady. It took me sooooooo long to get off (if you know what I mean) that the woman just hung up. And obviously, the call was on my nickle! Needless to say, I quickly dialed a new number to complete my experience. In total it was about 2 hours.