I believe that teachers and students should maintain a professional distance. I'm sure it's tempting for teachers to connect with their students using phone, email, and social media, but then the teacher risks becoming the students pal and eroding his authority. That might compromise his ability to grade impartially and exercise discipline when necessary. And teachers need some privacy, too. They don't want to be on call 24 hours a day. I used to teach in a boarding school and I speak from experience there.
Phone, email, and social networking contact between students and teachers should be restricted. There should be no online contact in social networking form between the two parties. It leaves too much room for informality. In addition, phone and email contact can become abusive too if a student doesn't know how to treat his or her teachers with respect.
Social media and other services can be a useful way for a teacher to remind students of work and to promote more learning. But, as many teachers would report any bad behavior over these services, I do not believe it would be used by many of the students in schools.
I do not believe phone, e-mail, and social networking contact between students and teachers should be restricted. I believe the rules regarding these interactions should be guided by the teacher and it should be considered fine for a teacher to allow varying communications. Personally, if I were a teacher I would encourage phone and e-mail communication, but would probably prefer texting for questions about the information being studied in class. I would not want to interact with students on social media. As a student, I would probably find a teacher that makes themselves available on social networking very devoted and easy to access if I have a question or need help with something.
I think people should be allowed to communicate on any platform they want to communicate as long as the normal laws apply. Why restrict students and teachers from talking on social networking sites? It makes no sense. Are they allowed to speak to each other in public? Very silly idea.