To me cell phones are redundant. I grew up with the internet, and I love wireless networking. I really don't see the point in making a call, when I can just click a button on an IM client and I have video and voice for free.
However, I seriously doubt people will leave calls on perminantly even if they are free unless an automatic hold feature is implemented. I mean what if you talk to your kids before you go to bed, do you really want your conversation in the morning to be, "Wow dad, you -really- satisfied mom last night!"
I can say it right now, 24/7 calls like fuck they're going to happen in my house. We had calls that was I believe $0.05 per call no matter the duration and I was on for up to 5 hours sometimes, but I -always- hung up because it's just damn creepy not to.