I flashed back to stock to try a few things (intially with 9, subsequently with 10) using MetroPCS (which may be the worst T-mobile MVNO I’ve run into).
At any rate, I’m running into a bit of an odd problem. The phone shows LTE, but drops to 3G/H+ when making a call (on stock firmware).
The enable VoLTE button is visible under network settings and is turned on.
In engineering mode ("##4636##") it shows:
Current Network: Metro by T-mobile
Roaming: Not Roaming
Data Service: Connected
Data Network Type: LTE
Voice Service: In Service
Voice Network Type: LTE
…
Set Preferred Network Type
LTE/UMTS auto (PRL)
…
Volte Provisioned is ON but grayed out
If I pick IMS service status, it says IMS Registration: Not Registered. Voice over LTE: Unavailable, Voice over Wifi: Unavailable
I’ve tried resetting the network settings, doesn’t change anything.
If this is what’s going on with the stock firmware (again, both 9 and 10) from Emma, this surely has implications for the future of VoLTE on Sailfish.