infringing on privacy
This is a question for me - certainly a five minute call at an unwelcome hour can be a pain - but when questions are left unanswered they can fester and end up with a student dropping. Up to this point I haven't minded the small inconveniences in exchange for the larger consequences of a drop - there might come a point when this is not so but, a stitch in time? What are your boundaries?
I think this goes along with teaching them professionalism. In most cases they would need to wait until a professionally appropriate time to communicate an issue. While it is very considerate to offer them assistance at any time, some might take advantage of this as well.
I think that's fair...I also ask each student for permission to list them in my phone so I know who is calling me.
For the most part, I have found students respect my time and only text/contact if needed. There have been some times when a student has texted me on weekends, etc. and I will respond that they can call me in the office on Monday if they want to have a conversation.