I've never written a note, I always just ring up and say they're not coming in for whatever reason. I always give a reason particularly if it's because of a particular illness. The school asks that we let them know of the illness so if several kids have the same thing & there is something going round they can put it in the newsletter.
Children who arrive later than 9.00 are asked to enter the school via the front door/office and let the office staff know they are there so they don't get marked absent.
A couple of times we've had dentist appts and the girls have been late and then I write a note the day before letting the teacher know they will be late the next day because the have a dentist appt - I have always just given the reason, never thought not too.