Many, and if I say like Sir Abhijeet Banerjee then (many, many, many, many, many ~ as counted Karan Thapar in interview with Wire) Watch here;(https://www.youtube.com/watch?v=ZQD-RwLDiz8) ..... :-) Respect!
If you are a teacher but still better comfortable with your old Keypad based phone than an iPhone now it's your turn now to learn new things. Online class delivery could be a challenge for MANY teachers especially those who are pretty used to write on a blackboard and maybe never opt for any other means of communication. In South Asia and especially India teachers will face bigger challenges being not technology savvy.
Learning a new thing is not that tricky. Online class delivery is really really fun once you learn it you will love doing it but the challenge is to do it right. To help teachers who all of a sudden are in dire need to deliver lectures online here is a link that I found while taking my daily dose of science.
The article is published in Nature.com website and not my property in anyways but I am sharing here to help out the teachers who need to deliver online classes. It's a worth read.