What is Gevey SIM ?
Gevey Turbo SIM as they call it is actually not a sim. It is a sim interposer.
An interposer is an electrical interface that directs the connection from one socket to another.
The purpose of a sim interposer in this case is tore-route a connectionto a different connection which can then unlock the iphone 4.
Gevey SIM Interposer is an integrated circuit which contains the unlock exploit using emergency number dialing [112].
The video below can explain the integration in a better way.

Here’s what to do to unlock:
Turn off the iPhone 4;
Place the adapter into the holder, on top put your micro-SIM;
Get the design insert in the iPhone, turn;
The status bar displays “No Signal”. Wait until its place appears the signal strength indicator;
When this happens, call the emergency 112 call, and resets after 2 seconds;
You go to Settings and turn Airplane Mode, and then turn it off;
iPhone displays the message “Error SIM-card” and then “SIM-card inserted.”Click OK, and then again turn on Airplane Mode and turn it off again;
“Error SIM-card reappears, but after a couple of seconds it will disappear and you will be able to use communication services. All this will need to do every time you reboot the phone.