[RLeeSimon]

ATT has whitelist online... will I need to go back from KEY² to Key¹ the latter being on the list?

[RLeeSimon]

T-Mobile will require VoLTE for all phones starting January 2021, AT&T to follow suit in February 2022 – Here’s what that means for you https://www.xda-developers.com/t-mob...s-shut-down-3g

[Dunt Dunt Dunt]

As with the other threads on this.... no body here knows for sure.

But one would assume if you have VoLTE now, you should be good to go.

But in the end we all have to wait and see.

[conite]

ATT has whitelist online... will I need to go back from KEY² to Key¹ the latter being on the list?

Only the AT&T-branded KEYᵒⁿᵉ is whitelisted.

[Chuck Finley69]

This says it all while saying we’re really not sure.

“If you have purchased a recent smartphone directly from AT&T or T-Mobile, then you very likely have nothing to worry about here. However, if you’re using an unlocked device or a device on a custom ROM, then you’ll want to pay attention to what’s coming. Since AT&T whitelists devices for VoLTE compatibility, you won’t be able to BYOD to the carrier starting February 2022 unless the carrier changes its practices or whitelists a lot more devices. There’s no reason they can’t—VoLTE is a standard protocol, after all—but thus far they haven’t. There’s nothing you, the device maker, or a custom ROM developer/modder can do about it.

While T-Mobile, on the other hand, doesn’t use a whitelist for VoLTE compatibility, many unlocked devices just straight up don’t support it regardless. The recently announced ASUS ROG Phone 3 does not currently support VoLTE on the network, for example. It’s not that these phones can’t support VoLTE on T-Mobile, it’s just that the device maker hasn’t done the work to outright support it. Modders on our ROG Phone II forums have figured out the steps needed to enable VoLTE on T-Mobile, proving that a little more work at the factory could enable support.

Theoretically, as long as your Android device has a working IMS (IP Multimedia Subsystem) stack, it should support VoLTE on T-Mobile (but not AT&T because of its whitelist system.) Typical Android devices with Qualcomm modems ship with a privileged application that bridges the radio interface layer (RIL) and the IMS, which developers take bundle in their custom ROMs to enable VoLTE support. LineageOS, for example, requires maintainers to support VoLTE if the stock ROM supports it. If the stock ROM doesn’t support it, then it’s unlikely you’ll be able to use the device on AT&T or T-Mobile once they shut down their 3G networks.

One more thing we need to talk about is support for phones purchased overseas. It’s likely that if your phone has the right hardware (which nearly all do) and the right IMS configuration (a bit iffier) to support VoLTE on T-Mobile and AT&T, then you’ll be able to make VoLTE calls on both networks, provided your carrier back home has a roaming agreement.“