This is a very safe unlocking method. You do not have to modify your phone's firmware in any way, so you do not loose warranty. You also do not run any external software on your handset so there is absolutely no risk of damaging it.
X-sim II (turbo sim) supports iPhone Version 1.1.2 sold in the USA. If you wish to use the phone in another country on other providers such as Vodafone, O2, Orange, Cable and Wireless, CosmOTE, Telcel, Rogers, Fido, Movistar, TIM, Movistar, Claro, SFR, Digicel, Bouygues, Optimus, Cincinnati Wireless, Cellular One, other compatible providers (iPhone lacks 3G support but is compatible with EDGE networks also known as 2.5G) How to check firmware version
Turn on your iphone, it gets "Slide for Emergency Call"
Slide and you will get the phone keypad
press * 3 0 0 1 # 1 2 3 4 5 # * and press CALL
Tap on VERSION