First, I'm going off on a bit of a rant here, and I want you to know it's not aimed at your daughters... they're just representative of the problem here...
270 dollars in long distance charges??!? For a KID??!? And over 600 bucks on your next bill?? Man, that's obscene; there was a time when I was engaged to a girl but working out of state one winter, and I regularly ran up 300 dollar phone bills, all of them to her... and friend, we used to talk for like 3 hours at a time... but I never came CLOSE to the kinds of phone bills you're talking about...
This society has become addicted to their telephones, and it's not a good thing... frankly, if I were in your situation, I'd take your kids' phones away, force them to get out into the real world and see what's out there...
Again, though, your girls are not unique... but their excuse is hilarious; they can't go without their phones long enough to allow them to recharge?? They can't recharge them overnight, while they sleep?? Or do they use the phones so flippin' much that a single charge won't last them the whole day??
Kids and adults alike need to get weaned off of their cell phones (said the man who refuses to own one)...
Now, for some practical advice; tell your girls that they're allowed to use your "house phone" to make long distance calls if they like (and why exactly are they making long distance calls, don't their friends live locally??), but they have to PAY FOR THEM when the bill comes in... and stick to it...
Watch how fast they stop making long distance calls on your house phone... LOL...