It is a little harder for those of us who transitioned from being students on teams (we are all friends with students on other teams) to being mentors.
Our team has a separate facebook group to which students can be added, along with a private team forum, and another facebook group for mentors only. There is also a google group we use because it seems a bit more professional. 3929 students don't add mentors on facebook or vice versa. As for phone calls and texts - students have our numbers but calling and texting is reserved for emergencies or when either the mentor or student is not at a computer and urgently needs information (about meeting time/location/transportation). We also make sure numbers are known so that students can call us when we travel to competitions for any emergencies.
We adhere to rules similar to what Al posted as well as all things listed here
http://www.atomicrobotics.com/wp-con...lEnrolForm.pdf
We also have background checks done on all mentors.
Its a very touchy subject, so many people have different views.