We use the landline still for incoming and outgoing calls. We both have mobiles too but I avoid giving the numbers out beyond family and close friends as I cant stand feeling obliged to have a conversation with the doctor for example, in the street!
If the mobile rings its really hard not to take the call, but if it rings at home when I'm out I can call back at my leisure.
Another thing I'd miss about the decline in landline use, is having conversations with your OH's friends and family occaisionally. If my sister rings and I'm in the garden Mr M will answer and have a chat while I come to the phone. Same with his family. If its all text or mobile calls, we'd lose that interaction.