I have tried many things to enable VoLTE on my unlocked (but T-Mobile branded) OnePlus 6T, including:
- SIM menu in Settings
- I have seen screenshots of other OnePlus 6T’s with an extra section containing a VoLTE toggle. Mine lacks this section entirely.
- secret debug menu in dialer (*#800#) (OnePlusLogKit)
- Like above, I have seen screenshots with an extra option for VoLTE that mine lacks.
- calling support
- The representative insisted my phone does not have VoLTE (https://www.t-mobile.com/support/devices/android/oneplus-6t/network-apn-and-volte-oneplus-6t) and that the 3G network is not shutting down (https://www.androidpolice.com/2020/07/25/t-mobile-will-soon-require-volte-on-all-phones-incomopatible-devices-kicked-off-january/).
I have confirmed that I do not see a VoLTE icon at any time and that my signal drops from LTE to 3G when making or receiving a call. I do have WiFi Calling enabled, however, if that narrows down the problem.
While searching for a solution to this, I did see a post (https://www.reddit.com/r/freedommobile/comments/9a2j2r/psa_getting_a_new_sim_made_volte_and_wifi_calling/) that suggests a new SIM might be the solution. I have had other phones prior to the 6T and never noticed VoLTE, and my SIM is from 2014.
Are there any other suggestions? Thanks.