[Xiaomi Mi A2 Lite Questions & Answers] Magendanz:
As has been documented on many XDA forums, we can make modifications to NVRAM on Qualcomm devices to unlock RF and LTE bands that have been disabled by the OEM. I decided to take a crack at this on the Mi A2 Lite with some mixed results, and am looking for suggestions. First of all, here are the "secret" phone codes that you'll need:

Enable Diagnostics Mode: *#*#717717#*#*

Info Menu: *#*#4636#*#*

From this last, there's a Phone Info section that allows you to set the Preferred Network Type. By default, this is LTE/UTS auto (PRL), where PRL stands for Preferred Roaming List. In the page menu, there's also Select Radio Band, which allows you to select either Automatic or United States.

For details on how to make changes to NVRAM on Qualcomm phones, I'll direct you to this thread for the Xiaomi Mi Note Pro. Here are the relevant values:

ID Desc Category Original Value Modified Value
01877 rf_bc_config CDMA 562950035735424 562950069289856
06828 lte_bc_config LTE 687195291871 1787696847071
65633 lte_band_pref System 0x000000A0000800DF 0x0000FFFFFFFFFFFF

ID Desc Category Original Value U.S. Automatic Cleared
00441 band_pref CDMA 0x0380 0x0000 0xFFFF 0xFFFF
00946 band_pref_16_31 System 0x04E8 0x04A8 0xBFFF 0x3FFF
02954 band_pref_32_63 System 131072 0 252116992 4294967295

For a better understanding of these values, I recommend this thread which includes RF band descriptions. Note that the band prefs (a.k.a. "forcings") can be cleared with Network Signal Guru (Cleared) or set with the Select Radio Band command (U.S. or Automatic).

Let's tackle the RF bands first. I used my Nexus 5X as a reference, since it was advertised by Google as having "universal" band support.

rf_bc_config (64-bit):
562950035735424 00000000 00000010 00000000 00000000 00000100 11101000 00000011 10000000 (Original)
562950069306247 00000000 00000010 00000000 00000000 00000110 11101000 01000011 10000111 (Nexus 5X)
562950069289856 00000000 00000010 00000000 00000000 00000110 11101000 00000011 10000000 (Modified)

band_pref (64-bit):
131072 0x04E8 0x0380 00000000 00000010 00000000 00000000 00000100 11101000 00000011 10000000 (Original)
0 0x04A8 0x0000 00000000 00000000 00000000 00000000 00000100 10101000 00000000 00000000 (U.S. Mode)
252116992 0xBFFF 0xFFFF 00001111 00000111 00000000 00000000 10111111 11111111 11111111 11111111 (Automatic)

So, we're just looking at unlocking the following RF band for T-Mobile support:

#25 WCDMA Band IV - US T-Mobile (AWS) (1700 MHz)

On LTE we're getting a bit more aggressive:

lte_bc_config (64-bit, of which 44 bits relevant): Bands Active:
687195291871 0000 10100000 00000000 00001000 00000000 11011111 1-5,7-8,20,38,40 (Original)
1099830990943 0001 00000000 00010011 00001001 00011000 01011111 1-5,7,12-13,17,20,25-26,29,41 (Nexus 5x)
1100502079583 0001 00000000 00111011 00001001 00011000 01011111 1-5,7,12-13,17,20,25-26,28-30,41 (Pixel)
1787698289887 0001 10100000 00111011 00011111 00011100 11011111 1-5,7-8,11-13,17-21,25-26,28-30,38,40-41 (Pixel 2)
1787696847071 0001 10100000 00111011 00001001 00011000 11011111	1-5,7-8,12-13,17,20,25-26,28-30,38,40-41 (Modified)
1787696847071 0001 10100000 00001000 00001000 00000000 11011111	1-5,7-8,20,28,38,40-41 (Actual)

My goal was to add LTE bands 12-13, 17, 25-26, 28-30 & 41, but as you can see I was only successfully able to add bands 28 & 41. In particular, LTE band 17 is critical to AT&T Wireless in the U.S.

Does anyone understand why some bands were unable to be unlocked, even after setting lte_band_pref to allow pretty much anything? Are there additional NVRAM settings that I missed, or is this due to lack of support in the power amplifier? Does anyone even know the model of power amplifier used in this phone?