In my opinion, having a cell phone now for 10 plus years, I would still want a landline for emergency purposes only. Kind of like a disaster device where no one else has one in the rubble but me and then I would have to sell the use of my landline because, since there's no power, everyone's cell phone batteries are dead.
Cell phone for everything, landline for back up only.
I will add another story to the bogging of cellular networks. At several Dave Matthews concerts and other large concerts I have been to, cell service is incredibly slow and often times non-existent because of the amount of people in one spot bouncing data and calls off of one or a few local towers.
Scenario: Disaster locally of some sort and you have 20,000 people gathered together for the purposes of survival all trying to use their cell phone simultaneously crushing the network. It's like having too many computers donwloading from the same connection. There's only a certain amount of bandwidth available at any given time and once that threshold is reached, we are out of luck.