Random or not?
Not random because you could only choose from the people on detention and not the whole school. Bias could occur because people on detention are more than likely to disagree with the existing rules.
Random as every student is on the list. Unbiased.
Random as every student is on the list. Unbiased unless you believe in astrology!
Not random as you are only selecting from Year 13 students. Biased as Year 13 students views on rules will differ considerably from younger students.

2. A day-time phone survey would not be good at producing a random sample for the following reasons:

Not everyone has a phone
Not everyone is home during the day
The phone may be busy
Not everyone who has a phone is listed in the telephone directory.

3. Ringing 250 people in each of the six main centres may not produce an accurate sample for all of the reasons given above in question 2, plus the fact that people outside of these six cities are also allowed to vote and their views would be ignored in the poll.

Easy to do and would not take much time, therefore cheaper. The people from the chosen department may enjoy working overtime or may be low paid and need to work overtime.
Easy and convenient to do. There may be a low turnout if ithe meeting is held after work. Because it is voluntary only the people with strong views either way could turn up so you get a biased result.
Everyone is asked their opinion. Expensive and time-consuming. Very few people often reply to written surveys.
Everyone would give their opinion. Time consuming. People may be afraid to give their true views in a face-to-face interview with the boss!
This would produce a random sample and take less time than interviewing everyone. For a small company the sample could be too small.