You must be kidding! Or very naive to even think that you could do such a thing.
I long ago stopped answering the phone in my home after school hours. I knew it was never for me. And that's okay. This is their time.
The phone is their lifeline. It is their constant connection to their friends (on the nights that sleeping over is a no go!). And their friends are all important.
We can't really force them to do their homework instead; they'll probably do it on their own schedule (late at night) anyway. Unless of course they want your help – in which case, you can make clear that your availability is at a much earlier point.
Like nature, teenage girls abhor a vacuum.
But the real question is why would you want to? It's not as if they were on the phone less, they'd spend more time at the Natural History Museum or browsing important photography exhibits or even doing volunteer work. (In fairness, they probably do some of that anyway.)
Like nature, teenage girls abhor a vacuum. If we limit their phone time, they will find other alternatives. They will go on the computer (if they have the option) with its inherent dangers. They will go to the mall – with its other inherent dangers. And those are the good and fairly "wholesome" alternatives. I don't need to delineate the kind of real trouble that teenage girls can, God forbid, get into – trouble that is all too easy to find.
Not only will they be looking to fill the time (no, they will not choose to just go to bed early) but they will be looking to fill the emotional space as well. That constant chattering on the phone to their girlfriends is an important emotional connection for our daughters. We don't want them searching for it elsewhere.
When I look around me at all the risks that teenagers take, at their foolhardy and sometimes self-destructive behaviors, at all the addictions and other issues that plague today's adolescents, I am grateful for the phone.
I am glad that is what my daughters are doing. Instead of trying to limit our teenage girls' phone time, we should appreciate that this is their "vice" of choice. One small glance around the world and you know you have nothing to complain about. And for a very small investment, you can purchase top quality ear plugs...