Sim not supported on unlocked device I have an Apple iPhone 6 A1586 from the US which was a replacement device from Apple, but the previous handset would've been locked to TMobile (always GSM and never CDMA I believe).

I've inserted a new UK (GSM) SIM into the device and it's telling me the SIM is unsupported. I've checked https://www.icloud.com/activationlock/ and this tells me the device is not locked and can be activated by a new user but I'm unable to do that.

I've wiped the phone and attempted to set it up as a new device but as soon as that new SIM goes into the phone it locks up saying "SIM not supported" but it will still work when I put the old TMobile SIM into it.

Any ideas? Am I missing something here?
You might need the carrier to unlock the device. 


https://support.apple.com/en-us/HT201328


Activation Lock in iCloud is to protect the owner of the device from theft. 

SIM Lock protects the carrier revenue stream as far as I can tell. Maybe there's another legitimate use for it that I haven't considered.