Well why would I? I don't go out that much so I have a deal that gives me line rental and broadband on the home phone and along with that I get free phone calls from my landline to ANY UK landline at ANY time on ANY day of the week. My phone bill is therefore £NIL despite me always being on it.
As I see it the mobile is only for use when I'm out of the house and unlike some people I do not make calls from my balcony or the pavement outside using my mobile whilst puffing a Marlboro Lite.
To be honest it's whatever suits your lifestyle. Most of my mobile calls are for less than a minute and are along the lines of "I'll be home at XX o'clock" or "I'm at the garage,/shops now. Do we need milk?"