My oldest just turned 9 and he's been getting phone calls from a friend from school. I probably should let him call that friend back, but well, he uses my cell phone and my battery is almost always at 20% battery life when we think about it, and it's MY phone. Sometimes, I just want to use it.
Back in the day, we had something called a landline. It was a universal phone for everyone in the house and the base was plugged into the wall. If you had a cordless phone, sometimes you'd have to worry about that phone being charged too, but if it was returned to it's base, and it wasn't lost, it wasn't a problem.