They all will work on iPhone 4 with preserved baseband using the 112 method. If you want the automatic unlock with Cydia, then spring for one of the Geveys in the hard package. Some require corner cutting where the black Gevey chip is to make room for the rest of your SIM card, so check the auctions for "No Cut." The ones in the hard package are more stable in that they don't drain battery more than 1% per hour. The others usually drain battery 2-3% per hour while idling. This one is pretty good, but you might need to jailbreak unless you're very fast after you dial 112 and push End. Usually, you have to double tap the Home Button to open the Phone app in the taskbar right before you push End Call in order to toggle Airplane Mode to On, wait for No SIM Card Installed, and then toggle Off. If No SIM Card Installed appears before you reach Airplane Mode, you need to restart the 112 process.
http://www.ebay.com/itm/Gevey-Ultra...330760005901?pt=SIM_Cards&hash=item4d02d5290d
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