Well, from an outsider's perspective, it seems like you might be acting unreasonably.

Your daughter ran up the phone bill. You asked her to stop. That means she's going to use another mode to communicate with her guy, and talking on the phone, or internet chatting, is the best she can do. (By the way, have you thought about getting Skype? It lets you talk on the phone using your computer, and it's totally free.)

Did she know that she isn't supposed to leave the house when it gets dark? If she didn't, then it's unfair to penalize her. Just have a normal conversation with her about safety and about being out late. Tell her that as long as she acts responsibly and reasonably, leaving and coming before a certain reasonable time, you won't impose a curfew, and that you believe she can act responsibly. Show her that you respect her ability to make good decisions for herself and start to shift the burden of caring for her safety onto her, so you don't have to worry about it all day and night.

The more you get in your teen's way, the more she is going to want to push you aside. If you give her a little freedom and show her that she can earn your respect and earn privileges by meeting certain reasonable expectations, she won't have as much reason to rebel.