UK: sms messaging here provides me with a uniform and universal way of contacting any mobile phone owner who want to be contacted, e.g. students I need to tell about a classroom change.
I just use a Web service like bulksms. In the UK and I believe Europe, receiving an sms message does not cost the recipient any money. I don't have to track who uses facebook and who uses twitter, they don't have to 'follow' or 'like' some institutional account.
That was the point I was making but didn't communicate effectively. There are a lot of different alternatives. Most of these alternatives are not 'push' but depend on the recipient monitoring something.
In the Further Education college I teach in, 98% of students have a mobile phone. Many of those are basic pay as you go dumb phones. Some feature phones, Blackberry phones are popular in UK with teenagers. A few have iPhones and Samsung and the LG slabby things. Not all have Web access on the phone (or have it but don't want to turn it on).
A result that surprised me was that teenagers don't access the Web that much on laptops or desktops.
The common denominator here is sms. I get 98% access. It costs a little money, but not huge. I hope it does not go away as we have brand (phone, carrier) dependent messaging.
SMS isn't going away, if anything it'll get cheaper as it's forced to compete with messaging apps. But if it goes away, e-mail can easily replace it for your needs (especially since most students have e-mail capable phones).