You'll get one call to let them know your address and then one more time to let them know information about graduation.
Letters, depends on your TI, our TI didnt let us write letter, well at least while he was around, so if you wanted to write you had to do it when he wasnt around, which was only while you were supposed to be sleeping.
So again depends on your TI, if your TI is cool, they'll have you use the phones while no one else is using them, but again it is a privilege.