My friend's iPhone is locked

If you have an Activation Lock, neither we (just users like you) nor Apple can help you, sorry.

Activation lock can be removed only by the previous owner, with the credentials that were used to activate that iPhone. Without those credentials, that device is useless to you.

Axel F.

The various definitions of “UNLOCK”

Unlock1: If you forgot the passcode to access the device ➔ If you forgot the passcode for your iPhone, iPad, or iPod touch, or your device is disabled

Unlock2: If you forgot your Apple ID password ➔ If you forgot your Apple ID password - Apple Support

Unlock3: Your device is locked to a different carrier and doesn't accept SIM cards from different carriers: only the carrier it is locked to can unlock it, if you're eligible.

Unlock4: If you have an Activation Lock, neither we (just users like you) nor Apple can help you, sorry.

Activation lock can be removed only by the previous owner, with the credentials that were used to activate that iPhone. Without those credentials, that device is useless to you.

Axel F.