When we went from dial up to DSL last year we went Verizon because their plan was no more expensive than our dial up. At the time, Comcast didn't have Internet in our area. Now they do. Plus, their plan is still more expensive than Verison's DSL, but dropping a land line, it's something to consider when our Verizon contract comes up in a few months. The difference will mostly be the difference in cost between our current 400 minutes a month and 'unlimited' calling. At present we don't even come close to using up those 400 minutes.
The thing to remember if you go off the phone grid is that you have no true 911 service. Cell phones are supposed to be able to provide location for emergencies, but I don't think this is very widespread yet. And internet-based phone service like Vonage warns you in the small print that your "911" service is not hooked up to your local 911 people.
SD