Can I unlock my iPhone with the IMEI number?
How to help a friend know if his or her iPhone is locked with iCloud using the iPhone IMEI
[Re-Titled by Moderator]
The only way to "unlock" an iPhone is by entering the correct passcode.
If your friend's screen says "Activation Locked" ... it IS.
If THAT's indeed the case, refer your friend to this article:
How to remove Activation Lock - Apple Support