Any sifus here know if a phone still doesn't support VoLTE on a telco network, which side is responsible to solve this, the telco or the manufacturer?

There are two ppl that I know are using TCL Plex on U Mobile, but they still can't enable VoLTE yet. They tried contacting U Mobile, but CS told them to contact TCL instead, and then when they contact TCL, the CS said awaiting response from software department and then no reply from CS after 1 month.

Funny thing is that I heard other TCL Plex users on Unifi Mobile and Digi can get VoLTE, but not on U Mobile.

Prepaid U40 plan comes with 3GB high speed hotspot, followed by unlimited hotspot at 6Mbps.