Your smartphone is not locked by a physical switch. The lock is a digital restriction enforced by two primary databases:
What it is
A phone unlocking server is a remote database that interacts with your device's operating system or your network carrier's infrastructure. When a phone is "carrier-locked," it means the software is restricted to reading SIM cards from only one specific provider.
If you input credit card details for a "temporary holding fee" on a free site, you will likely see unauthorized charges on your account later. Legitimate Ways to Unlock Your Phone Safely