I am a new high school teacher in a major city teaching urban children. A colleague of mine uses her personal cell phone when she needs to call parents, but most of my current coworkers deliberately use the school phone to call parents. I realize safety may be an issue using my personal number (though it seems low-risk), but convenience is sacrificed using the school phone. There are no school or union policies on this issue. I am wondering if there are any factors to whether I should use the school phone or my personal number that I am not considering.
It's best to keep work and home life separate, particular as a teacher since you're dealing with children and families.
Most schools will not give out a teachers personal number to a parent unless there is an urgent pressing need for it. There are several good reasons behind this rather than it being arbitrary.
First and foremost is that the child is a pupil of the school and any interaction between parents and teacher should be done via the school for the safety of the teacher, the family AND the school. The teacher is an employee of the school, not the parents. So the two should only interact in controlled circumstances in normal work. There should be no need for private interaction outside of an emergency situation. And there should be no emergency situation outside of school hours when the child is under the physical supervision of the teacher.
So in the absence of any protocols against it, it's still best to go with the school as an intermediary rather than give out your number. Low risk is a matter of perception. It would only take one incident, however twisted, to potentially kill both your career and reputation.
I don't know if this works in your country, but in France we can temporarily mask our phone number when dialing someone, by pressing #31# before the phone number you want to dial. For example you want to dial 123-456-789, you then call #31#123-456-789.
Doing so, you can call any parent you want using your own mobile phone, but without letting them know your phone number. If you need the parent to call back, let them know they can call the school and they will put you through.
Many people don't give their private phone number to their employer, because work is work and private is private. My employer has my phone number, so they can contact me if there is an emergency, and they know what is an emergency and what isn't, so that's fine.
In your case, you are thinking about giving your phone number to a bunch of people who you know nothing about. They are people that you can't expect to behave professionally, because they are not professional. Don't do it.
Do you think they should, or shouldn't, be able to call you with after-hours issues?
If they shouldn't, don't give them your personal phone.
If you trust them not to abuse it, or if you are willing to not answer or tell them to call back at a better time, you could give them the cell number.
I really don't think the other concerns are as significant as this one.
I don't know how it is at your school.
But at my work all calls are recorded. (This is legal where I live.) For me that's a big reason to never have conversations with clients(parents) on my personal phone. (or basically any cellphone.) That way whenever there are misunderstandings you can always listen back the call. Also, because it's recorded it makes you think better about what you say.