This is interesting... I'm not as negative as the rest of the group seems to be, but maybe that's because I think cell phone service is a rip off already. This would actually save me money if I switched now, but I would lose the unlimited data plan. Maybe I care, maybe I don't. I have very rarely gone over 2GB, and my wife never has so we could likely share 4GB. But we have 2 kids getting to the age where my wife thinks they need cell phones (and they think they need iphones). Assuming they get dumb phones now, that's an extra $20 a month, plus we bump up to the unlimited family text plan for another $10. And that is a reasonable amount. Especially since we shouldn't have to bump up our minutes because they would mostly be calling us and those minutes don't count. It would cost twice that to add two dumb phones in the share everything plan. But the overall price difference is only $10 more. And as they start to use more minutes, and our third child get's old enough to have a phone, I could ultimately see it being a real savings. Depending on data usage I suppose.
Paying an additional $10 for a tablet or laptop doesn't make sense. Except it is a proprietary network, and they can charge you to access it. Similar to how extra cable/satalite boxes cost money (I realize it is a rental cost usually, not something you own, but I feel the idea is similar). Right now to add a tablet, you are paying an additional $130 premium (in the case of the ipad) + $30/month for a 3G/4G tablet. That doesn't make sense to me either. With the share everything plan, it is $0 extra for my phone to be a wireless hotspot, and now all of our wi-fi iPads, iPods, Kindles and portable gaming devices have access wherever we are. Right now, that would also be an additional data plan.
I don't think these are the only plans they will have, (the old plans aren't going away) and obviously how much sense it makes depends on the individual situation. But I like it as an option.