Yeah it's not down to what SIM card you have in the phone, if the phone is factory unlocked and from samsung it will be BTU (which is just the software on the phone) my phone was originally bought on contract with three, so I had bloatware, and logo on bootup etc, but I was running a slightly different software on my phone, each network like to have Thier own stuff built into the software, meaning it's not just stock software like you get on SIM free/bought directly from samsung, I flashed BTU on my phone and it's now allowed me to be eligible for the beta as I now have stock firmware and I follow the BTU/XEU update path, this is also the reason why you sometimes have to wait ages for updates on certain networks as they can be very slow to do what they want to do to the updates.
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