This app was mentioned in 5 comments, with an average of 1.20 upvotes
Yes, OTA updates are not dependent on which network you are connected to. A phone without a sim card connected to WiFi would still download/install an OTA when available.
Visual Voicemail is baked into Android 6.0+ for T-Mobile, but also available through their Visual Voicemail Android app. Metro has its own Visual Voicemail app that you would most likely need to use instead, but you would still get VVM.
Metro PCS uses the T-Mobile network with the same exact frequencies/bands. There will be no network issues using your T-Mobile Note 4 on Metro.
Good point. I do, which is the carrier's Visual Voicemail app, which is getting complaints recently -- but for not sync'ing properly, but not for this specific error message. But there is suspicion there.
MetroPCS I would think would work, though I don't know 100%. But my wife has a MetroPCS branded phone and it supports all those features. VVM is just through an app that you can download in the Play Store (not integrated into the dialer, but the next best thing) so I don't see why it wouldn't work.
Well have you tried downloading the Visual Voicemail app? https://play.google.com/store/apps/details?id=com.metropcs.service.vvm