8-digit password prompt only when SIM is in device (it's not the PUK) My HTC A9 phone is asking me for an 8-digits password only when a SIM is in the device. I already tried it with the PUK of the SIM what does not work. If there is no SIM in the device, there is no password prompt and I can use the phone normally. With no SIM in the device, I did a factory reset of the phone, but nothing changed.

The password prompt says: "Network locked". Is this a SIM-locked phone?

What is going on here?
Since the PUK does not work (which usually would only be asked if the PIN has been entered wrong three times) and the prompt says "Network locked" this is most likely a SIM-Lock of the phone by the carrier.

Using a SIM from the carrier the phone is branded with you should not get this prompt and it should simply work, to use a SIM card from another carrier you will need the unlock code.

You can get this code from the carrier, most carriers charge only a very small amount or nothing at all after some period of time.