This is maybe where the Discourse push notification feature topic for the mobile app can be brought back to the surface.
We have a highly regrettable trend in our days of Whatsapp groups that forces people to have their phone numbers public if they simply want to get info over local sports community events. 
This should just not be ! Especially for women.
And regarding @justinm concerns for reachability : having an app started in background when you start your phone and providing push is one of the best way to reach people(with an opt-in option for sure).
Now I don’t know the workload for this, but people will be willing for more related features like mentioned in the above topic : view the source of the push when you subscribe to multi forums, choice for sound and/or vibration according to selected categories etc.
Interesting mobile app push notifications related topics :
iOS Mobile App Notifications and How to Implement Push Notifications for Our White-Label App (Rebranded)