My husband and I have been strictly cell phones for the past 4 years. before that we had both the landline and the cells.
The landline was barely used and we felt that it wasn't worth keeping at the time because we rarely used it and using just cells have worked out just fine for us.
But now that our daughter is 10 and is constantly using my cell to talk to her friends (plus she has one friend that calls non-stop thinking that my phone belongs to my daughter), we are considering getting a broadband phone connection (we have WOW for cable and internet and they offer phone services too) because we feel that she isn't old enough for her own cell yet (besides, all 3 of my kids can't even keep track of their own gammeboys right now) and my boys (15 yo Aspie and 8 yr old) are just starting to use the phone too, just not as much as their sister. Also, When the kids are home on nights that I have to teach and dad has to work,(my 15 yo is a very good "kid sitter" actually) I won't have to leave my cell phone at home with them for emergencies.
I think that it really depends on the situation on whether or not to go cell phone only or landline and cell phone.