I'd definitely keep the phone from night until morning. Besides that, blocking the texting capability may be appropriate. At one point, I blocked every feature from difficult child's phone except the "make a phone call" option. When I restored some of those features, I told her she had to show me all pictures sent or received before deleting them, and that if she deleted anything without permission I would assume it was inappropriate and take the phone away. The phone company printout showed clearly when pictures were sent or received. Same with texts, although I don't remember putting that particular rule on texts. I see no problem with doing that though, because the fact is that once an electronic message is sent, it is NOT private. As much as I explained that to difficult child, she never seemed to "get it." Messages were passed around and forwarded frequently at school.
I also made use of the parental controls available for cell phones, and I'm sure those controls are even more advanced now. I used features such as the GPS that sent me a message if difficult child went outside a certain radius of where she was supposed to be. I also used the "locate phone" option that actually gave me a map of the phone's current location and the direction and speed at which "the phone" was traveling. I set times when the texting feature would be inoperable--such as during school hours. That feature would still allow texting between "trusted numbers" that I set, meaning I could communicate with her by text even when that feature would not work otherwise. I wished the same restriction was possible for voice calls, but at that time it was not. Maybe it is now though--or will be soon. Gradually, gradually...I think technology for PARENTS is catching up to the technology that has given our teens so much power. Of course, it's impossible to get around the fact that a teen can simply borrow a friend's phone to bypass all the restrictions. You can do only so much.... Don't forget that for middle-of-the-night phone conversations, she can simply use the home phone while you're asleep unless you somehow control for that possibility. Mine did. At one point, I was locking up all the phone handsets with me overnight, and I also disabled the phone jack in difficult child's bedroom. It really was insanity for me, trying to stay one step ahead. I felt like I was managing a prison instead of a home.
Eavesdropping on phone conversations is very time-consuming, and chances are that you will miss important pieces. It's much easier to take the phone away, put a surveillance program on the computer, and let her use the computer. If you put no restrictions on the computer, while you have many restrictions on the phone, it is likely that she will use the computer. I have no ethical problem with that tactic if you have good reason to be suspicious and it's the only way to get to the truth and try to keep her safe. Especially after you put her on notice that any electronic transmission is then in "public space" ... that the concept of privacy of electronic communications is an illusion... I think it's a fair playing field. E-Blaster--already mentioned--is a good one.
It's so impossible to prevent all the behaviors you wish you could prevent. Definitely the birth control is very important but can also be difficult for you to control. difficult child's doctor refused to do the depo injections because of family history of osteoporosis. I monitored the birth control regimen best I could, but there's simply no way to be SURE your daughter is consistent unless you're going to become a true drug warden--watch her take it and check her mouth to see that she swallowed it. My difficult child still insists she took the pills EXACTLY like she was supposed to and got pregnant anyway. I know better. As soon as she insisted on moving the pill-pak from the kitchen cabinet to her purse, I knew what would happen next.
I'd say do as much as you can for as long as you can. Hopefully she'll mature enough to make wiser decisons before she finds loopholes through all your safeguards. Beware the danger, though, that your life can literally be overtaken by the constant monitoring, trying to run interference, and struggling for damage control.
