I see from your reply how you have a vast experience of (graciously) managing personnel in activities that run 24/7 (please read shifts) and that your employees at home or in vacation simply love to be notified about how the internet at the office is working.
Or Canada is different, probably here I would be called out for anti-union behaviour or even stalking. 
Besides I would need a mass SMS send program on my own phone (no internet, you remember? 
).
I could upload to a cloud server a database of the timetables for shifts and holidays and then connect to it[1] and run a query to determine the phone numbers to send SMS to, of course.
[1] no, wait … 