My family is one of the only families, potentially on Earth and not just in the USA, who has only one phone in the entirety of the house. We have cell phones, sure, but when it comes to the land line, there's only one, and it's in the kitchen.
Our house has an open layout, and the kitchen is at the center of the home. The net result of this is that anyone using the landline can be heard clearly and loudly throughout the entire house. The effect is not that different from sitting next to a really irritating cell phone user when you're stuck on the train or walking behind them on the sidewalk - you're hearing one side of a conversation, and it ain't interesting.
When someone is on the phone, no one else in the house can make any noise. Why? Because then the person on the phone can't hear their own conversation (again due to the nature of our house). So that means no TV, no typing too loudly on the computer, and no having your own cell phone conversation anywhere on the first floor.
The TV is another issue - it's located in our family room, the only room with slightly more potential to generate house-filling noise than the kitchen. Thanks, friendly architect! When someone is watching TV here, it permeates the pores of your skin and makes your intestines shake. And when your dear father is hard of hearing, wearing earplugs around the house doesn't seem like the weirdest idea anymore.
Since I'm being a huge bizatch today, my mom is making phone calls so that she can achieve her appropriate human interaction quota. Unfortunately, that is making me grouchy since I'm trying to have a quiet day, but I can hear her conversations throughout our house. Maybe I'll have a bowling lane installed in my room, and that'll solve everyone's problems!