My wife runs a clinic with about a dozen health care providers. They use a paging service that delivers pages to a phone app. It has to be a phone app because the shifts are 24hrs and the providers sleep when they can and need to be able to turn off all other notifications.

This costs about $12,000/yr and uses servers in the United States. Some of the staff work very part time, but still need a license at the same cost even if they only get one or two call shifts a month. The price ratchets up regularly.

There is competition, but nothing really better.

I could stand up an asterisk server and write a simple Android and iOS app for an ongoing cost two orders of magnitude lower (using existing infrastructure), but the app store impedance is too high to risk it.

I don't have the practical ability to confidently get an app into the Google play store and the Apple app store and keep it there.

The only viable alternative to bending over for these vendors for us is to go back to discrete pagers. It may come to that.