How do professionals unlock iPhones using the serial without having the mobile in hand?
Unlike most other devices the lock is not maintained on the iOS device itself but on the Apple iTunes Server. Whenever you connect your phone to iTunes, or restore it the server is contacted to retrieve this information.
So for a legitimate unlock a request is sent to the iTunes server along with the phones serial number where it will be validated and then stored. The device itself is not necessary for this.
Thank you for answer. does Apple allow this action or the team hacks iTune server and change the state of the phone permanently ?
second question who is best prices, reliable teams ?
because i know there is scam advertisements.
I don't think they are hacking the iTunes server. More likely they gained access to the system used by some provider, former employee or so? Also I don't think Apple concerns themselves with it as a provider lock is only in the benefit of the provider, not Apple. That's why Apple is selling them unlocked through their own shops.
Both, the best price and most reliable way is probably going to be the provider the phone is locked to.
Unless the policy has changed both, Sprint and Verizon will unlock the phone free of charge as long as the contract is fulfilled and in good standing (no open bills or something).
T-Mobile has a similar policy although in some regions they do charge even when the contract was fulfilled.
So my first suggestion would be to contact the provider. I can't make any recommendations on the internet as I haven't used any of them.