All Apple iOS 7 devices including the iPhone 5s and iPhone 5c, carry a new security feature called Activation Lock which is linked to Find My iPhone.
When submitting a device for fault resolution, the Activation Lock feature must be turned off. If this feature is not disabled before its submission, it may affect the ability to receive an exchange replacement and transfer their warranty and settings.
Only your Apple ID and their password can deactivate this feature.
To remove the Activation Lock, you will need to go to the devices settings for iCloud or Find My Phone and deactivate. This must be done prior to returning your phone.
If you have already submitted your device, you can deactivate the Activation Lock feature remotely via web on www.icloud.com
If the device does not power up, please visit www.icloud.com and disable it remotely.