We have been without a landline for about 5 months and can't tell the difference. I transferred our home number to my cell phone "just in case."
But no one really used our home phone anymore because they could always reach us on our cells. In fact, whenever they DID call our home number, no one ever answers and it goes to the machine because the batteries on the cordless phones are low/dead and don't recharge well so we never hear the phone even ring.
We also always use our cells for calling out because it is more convenient and because of the lack of juice on the cordless landline phone. So, we make about 1 call out a month, if that.
We DO have small children, 6 and 8 but they are NEVER home without us. If we are not home, they are either with us or at my Parents' home.
We had been wanting to cut landline service for YEARS, but were reluctant because of the trouble getting through on cell service in NYC during 9/11 and the black and brown outs.
HOWEVER, my parents live in the next building and we would just be calling each other. What pushed me over was that worst case scenerio, I could just go over to let them know we were ok and to use their landline, if necessary.
As I said, there has been no difference for us, I can't even tell (since we weren't using the landline anyways), except I have one less bill to pay per month!