Someone just told me about this and I did not know that these calls with the phone icon were free.
I made a call yesterday and it was just as good as on my mobile to mobile. You can phone anywhere at no charge.
I didn't know about this but as I loathe and detest using Messenger that's no surprise.... I avoid using it altogether and only check my FB messages when on my laptop. To be honest, I very rarely use a mobile to make phone calls anyway, that's what my home phone is for and then they are free as part of the package!