Running ultrasn0w is almost as easy as running the browser-based JailbreakMe exploit.
To get started with unlocking your iPhone you’ll need to jailbreak it first. Follow the instructions in our iPhone 4 jailbreak article (it’s extremely easy).
Then download the ultrasn0w app from Cydia (the jailbreak version of the App Store) install it and once it’s complete you can use a SIM card from any carrier. It’s that simple!
If your iPhone 4 was previously activated with another carrier you may need to change the APN settings to get it connected to the new carrier’s data network. If there’s no option to change the APN through Settings > General > Network > Cellular Data Network you’ll need to connect the iPhone to the Internet over a Wi-Fi connection and point the Safari browser at http://unlockit.co.nz. Use the Custom APN option and select your carrier then hit the ‘Create Profile’ button. This will create a Configuration Profile that you can install to your iPhone to enable data.
So why go to the trouble of jailbreaking and unlocking when you can simply ask your carrier to unlock it for you? We previously covered the cost of unlocking an iPhone 4 bought through a carrier Telstra is the only network that charges an unlocking fee ($150) but even if you get a free unlock through your carrier it may take a while to be processed. If last year’s iPhone 3GS launch is any indication an unlock request can take up to 14 days to go through.