Unknown "________ would like to send a message to 45567" notification I keep getting these random SMS permission notifications. The app or service requesting to send the message is always changing.


Pixel 2 XL on Android 9 on Freedom Mobile in Canada. 
Play Protect and Malwarebytes don't detect any malicious apps.


How do I determine what's causing this?
Looks like this is an issue specific to Freedom Mobile users happening since May 9, 2019. Possibly caused by a software update from Freedom around that time, it appears to affect Google Phone (beta) users with Visual Voicemail enabled.



Background

There is a thread on Google's official support for Pixel Phone, which mentions the same issue about some multiple random processes requesting permission to send an SMS to 45567 on multiple setups:


Device model: Pixel 2, Pixel 2 XL, Pixel 3, Pixel 3 XL, 
Android version: Pie, Q (beta)
Process name: com.android.sdm.plugin, Connectivity manager, Oemdmtrigger, com.qualcomm.data, uceShimService, Phone and Messaging St..., Modem Service, SDMService, [etc.]
Software update: After the May security patch, or after an update to "Carrier Services" and "Actions Services" but before the May security patch.


Temporary fix/workaround

As per Matthew Naugler Klassen's post, the (temporary) fix is to disable Visual Voicemail in Google's Phone app:


Open Phone app
Open Settings
Under Voicemail, disable Visual Voicemail


Additional Remarks

Freedom Mobile seems to aware and has acknowledged the issue, promising to escalate it and deliver the fix as soon as possible.