Is this carrier locked or iCloud Activation locked ?
If carrier locked, device can be unlocked easily. But if it is iCloud Activation locked, then it is a pretty tough process to unlock. Most of the online services that promise to remove activation locks are a scam. Activation lock is directly from Apple's servers. That is a featuredesigned to prevent anyone else from using the device if it's ever lost or stolen. Only way to unlock is to contact the owner and get the Apple ID and password of the account.