I found an answer from another question thread. This works on Android 8.0.0 Oreo on my V30, not sure about others:Go to Settings, select General.Select Apps and Notifications.Select App Info.In the 3-dots menu on the upper right, select Show system.Scroll down, tap Wi-Fi Calling (this only appears if you first select show system apps).Tap App NotificationsUnder Categories, tap the 3 dots next to Calls will be made over Wi-FiTap ImportanceChange the selection to Low (No sound or visual interruption).This doesn't turn off the notification entirely, but it does get rid of the noise or vibration. You'll still see the notification if you pull down the notification pane, but this gets rid of the noise or vibration, which was the most annoying part, since it kept prompting me to pick up my phone to check notifications, only to find this notification again.
It was especially bad when I posted this question. My home internet connection seemed to be having problems. I was trying to stream video, and it kept freezing, and at the same time, my phone kept giving me these "Calls will be made over Wi-Fi" alerts, probably because the Wi-Fi connection was intermittent. I'm now trying defaulting calling to cellular, but I can't turn off Wi-Fi calling entirely, because I lose cellular signal indoors where I work. I need both cellular and Wi-Fi calling because I don't always have cellular coverage, and can't always be on Wi-Fi.
Thanks. I was hoping for a better answer, since this alert mars what's otherwise a nice phone (I get too many of these useless interruptions). I'll try that, but I think I may still get lots of alerts if I set cellular as preferred. T-Mobile's signal doesn't penetrate the building where I work well, and I have to depend on Wi-Fi. When I move near the windows of the building I get cellular service, but when I move to the center of the building I usually lose signal. I expect I may get alerts whenever I move around in the building if I make cellular preferred.
Another update, I think I've solved this. In case anyone else sees this this is how I fixed it:I went into the Play Store, and uninstalled the updates to the T-Mobile app. (Uninstalling the app entirely wasn't an option in the settings menu, but the play store allowed me to uninstall updates). I then opened the app, and it promoted me to install the updates again. That happened. This time, I deselected collecting diagnostic and network info. The app now works the same as before, but it appears it's not draining my battery anymore. The battery info in the Android settings menu only shows 2% for this app, which is where it was before I uninstalled and re-installed the updates 9 hours ago.I still don't know if selecting collection of diagnostic or network info that I allowed a month ago was causing this battery drain, or why I didn't seem to be able to stop it in the app settings, but reinstalling the updates has fixed this.
The app version is T-Mobile 7.10.1.94, if that helps.
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