Cell phone, landline, or both?
Both. I work from home and really love my landline's headset which I need to use for hours on end every day. Plus, the reception is excellent. I don't give out the number - I have a Google Voice number that I use for everything except personal friends who get my mobile number.
Do land lines still exist everywhere?
Both. When I’m at home I use the landline. My phone line provider does my internet connection too. I keep my mobile (cell phone) for when I’m out and about.
Both. The landline is screened 100% of the time and is the number I use for all forms I need to fill out. My cell phone I only give to people I know and for job applications.