Who would want a high-end smart phone if they cant use it? Anyone would want that if its free but not if there is a fee. So if you are giving a mobile phone to someone as a present, he or she will appreciate it more if its already unlocked. Same thing when you are selling it. An unlocked handset has higher value than to those that are locked.
There are some softwares available on-line that can unlock mobile phones for free but they are too risky to use. Most mobile phones just have 10 attempts for you to enter the unlocking code and when you exceed to that your phone will totally lock to the original network provider so be careful on choosing one. There are also some companies that offer this service for a certain amount which I would suggest you to do. But before buying their service, please review the company's history and their Terms and Conditions.