Found this for Region (I think the ‘baseband version’ helped me find the below correct code listed on one of the Firmware links you listed above):
BTU (unbranded), EVR (EE), BTC, CPW (Carphone Warehouse), H3G, O2I, O2U (O2), ORA (Orange), OXA, TMU (T-Mobile), TSC, VIR, VOD (Vodafone), XEU (EE & Three)
I think I need a cheap spare smartphone to experiment with, are there any you recommend ?, I’m pondering purchasing another S7 but without the Echo issue, as its cheap and small, but only if there’s no security risk in using it with older Vendor SPL.
The Echo it seems is an undefinable problem:
This problem does not impact all users of this phone.