I have a cell phone because:
I share a house with family and two land lines were a pain in the rear. One person does not like to answer the phone so lets the machine get it all the time and someone else uses it a lot for buisness. I prefer to have my own number.
My family and I are all on different schedules and sometimes it's easier to call or text for a question than it is to wait untill I actually see them.
I help with my nephews and sometimes someone who is not home needs information quickly. Between ex-sil, brother, brother's girlfriend, mom, stepdad, me and the twins (who have phones) and thier maternal grandparents schedules have a habit of changing hour to hour.
At least four members of the family travel frequently all around the metro for work.
All of us travel and nationwide long distance is lovely.
My dad and best friend would be long distance calls in state without cell plans.
We do take road trips a few times a year and the side of the road is a lousy time to decide that a cell phone might be a good idea after all.
AAA, GPS and a cell phone are good travel companions.
All I can think of for now.
and as an aside. I had a cell phone in the early 90's. Then got rid of it. Carried a pager for a few years. I did not have another phone until around 2000, when my mom insisted that I have one as I was going to attend graduate school and communting and I was also going to be keeping my nephews 5 days a week. Before that I didn't worry about having one or not. It made her feel better, I still have that line and we still share a family plan it's cheap for all of us (stepdad, her and me) to share and we never go over our minutes.