The good news: The device supports T-Mobile's LTE band and registers/displays LTE.
The bad news: The LTE implementation does not seem to be at all reliable when on a GSM-based network.
1) I had a hell of a time trying to get it to accept a GSM conditional call forwarding code -- it would just immediately close the Phone app and I would temporarily lose mobile data connectivity. When I disabled LTE, it worked.
2) When I make a call while on LTE, the mobile data drops as soon as I dial. Google Voice dialing never works (app immediately closes with no mobile data) and standard dialing often just immediately closes the phone app. If I re-initiate the call after the LTE connection has dropped and before it recovers, it will sometimes work.
All of this is resolved when I force the phone into 3G-only mode. From an HSPA connection, both of the above seem to work fine.
My theory on this (maybe I'm off base) is that the handoff/fallback that's required for the phone to use a CDMA network for voice while on an LTE network is somehow still triggering -- and obviously not working for GSM.
Things I have tried:
- Setting preferred network mode to " LTE / GSM / UMTS "
- Resetting APN settings
- Clear Dalvik and Android caches
- Disabling Xposed framework
Things of note:
When I boot the phone for the first time, I receive this message:
"Sorry - This SIM card is from an unknown source"
After I acknowledge it, no problems other than the above.
Would love some pointers on what I could try to resolve this... anybody else have this scenario and had issues like this -- or gotten it working?