Okay you start by saying developers can't add this ability and go on to say it can be done in the same sentence?
The fact that you and some developers don't know how to get that status is no proof that others don't know. Or do you honestly believe that MS has created the ability but is actively preventing its use?
Well, I'm only reporting what I've been told by the programming experts. I agree with you that it all seems pretty bizarre. But I can show you the proof.
My first step was to see if I could interrogate the SMS app. Here is the link to the forum where I ask the original question:
https://social.msdn.microsoft.com/Forums/windowsapps/en-US/e651f3e0-b00d-4aad-acfe-1c80c080a662/uwpmonitoring-sms-notifications?forum=wpdevelop#e651f3e0-b00d-4aad-acfe-1c80c080a662
The key phrase is this: "Windows.ApplicationModel.Chat API is the key point, but this API is not available to all Windows/Windows Phone apps. Unless your developer account is specially provisioned by Microsoft, calls to these APIs will fail at runtime." Later on in the thread I'm told to contact Microsoft Developer Support to find out how to get this special status, but it looks like it will need me to sign up for paid support, which I'm reluctant to do just now, especially if they then say "No"!
My second approach was to see if I could interrogate the Notification Centre instead. Here is the link:
https://social.msdn.microsoft.com/Forums/windowsapps/en-US/bcbcce5d-1041-419e-9915-beeb93637d48/uwpcan-i-interrogate-the-notificationaction-centre-programmatically?forum=wpdevelop
You will see that I am advised that there is no way an app can read notifications from other apps, only from itself. Later on I am told: " It is not possible because there is no API which can read the notification from notification center."
Thirdly, I think my enquiries must have kicked off an interest in someone else, because they started a new topic which I joined:
https://social.msdn.microsoft.com/Forums/windowsapps/en-US/450affed-1dba-48b8-9d8c-40d1bc94da75/a-sms-reminder-app-?forum=wpdevelop
During the discussion I found something called "system triggers", one of which is called "SMSReceived". These can be used to launch a background app, and I wondered if the background app could then generate the repeating beeps. A contributor said he'd experiment but he hasn't come back to the thread.
So you can see that I've tried damned hard to find a way of doing it myself - it's not like I've been sitting on my arse making demands and expecting others to meet them.
To answer your original point, HoosierDaddy, it looks like Microsoft have indeed added this ability, but have then blocked it to all but those developers to whom Microsoft grants a special status. I guess this is all to do with security and privacy. And right now, unless I pay for a support contract, it looks like I can't make a direct request for this special status.
Even then, I'd still have to teach myself how to program for Windows Mobile! :grin: