my phone is locked

What do you mean by "unlock"? There's 3 kinds.

How to unlock your iPhone - http://support.apple.com/HT201328 - Only some carriers offer the ability to unlock iPhone for use on any carrier. Follow the instructions in this article to unlock your iPhone.

iCloud: Activation Lock - http://support.apple.com/kb/PH13695 - This is a security feature so only legitimate (i.e., not stolen) redistribution of devices is possible.

Turn off Find My iPhone Activation Lock - https://support.apple.com/HT201441 - If an activation lock was put on a device, only the owner of the account that applied the lock can remove it. Get them to remove it or return the item for a refund.

If you forgot the passcode for your iPhone, iPad, or iPod touch, or your device is disabled - https://support.apple.com/HT204306

More information would help. How is it locked? Activation locked? Disabled? What have you tried to make it work?

Activation Lock - Turn off Find My iPhone

Passcode - If you forgot the passcode for your iPhone, iPad, or iPod touch, or your device is disabled

Edit -Limnos beat me to the post.