i am unsure if this would benefit or help anyone on tmobile usa, but could we push the deutsche telekom software to the unlocked devices purchased in the united states to utilize hd voice and vvm? anyway to test this?
You could flash the Deutsche Telekom ROM onto the US variant as long as the frequencies and variants match. Also HD voice and VVM is a carrier feature and may be dependent on the carrier to enable it first. Historically, VVM and HD voice had always worked for me on unlocked Lumias running WP 8.1.
thank you for the quick responses, i'm using the duel sim unlocked, unbranded 950 xl. currently i receive band 12, but no volte. im wondering since im under the understanding that the device is the same as the tmobile uk, it might be possible to flash that rom, since it has hd voice and uses the same bands as here in the us, while also enabling volte. just nervous about spending the next 2 days unbricking my device. i guess i am still within the 30 day return policy