S.R.
I have a landline for a couple reasons:
I like to have a central "home base" for school forms and stuff- so all the robo-calls from the elementary school come to the home line for us all to hear.
I like to be able to be on long phone calls around the house hands-free (I hate that I can't cradle a cell phone on my shoulder).
I like to be able to grab a phone in any room (I have like 4 cordless phones for my landline).
I want me and my kids to be able to call 911 quickly and easily at any time.
That last one was validated to me when my sister and her husband had a crazy crack addict show up at their door trying to get in. They called 911 from their cells and there were a lot of issues with that, like 911 being able to trace their location immediately, call them back, etc. She got a landline the next day. (in case you are wondering, the crazy person passed out on their doorstep before police even got there, but the 911 operater told them the police were at her door, so she opened it, and the passed-out crack addict who was leaning against the door fell into their home. Yeah, the police were not there yet. That part has nothing to do with the cell vs. landline issue, just thought you might enjoy that tidbit.)
The sales calls do get annoying though.