Hardware unlock for iPhone 4
Gevey has released a SIM Interposer which can unlock the iPhone up to iOS 4.3 by force activating the baseband using the emergency dialer.
SIM Interposer works by adding a EEPROM chip to your SIM card just like a TurboSIM. The unlock uses the ability to call 112, a number that can be called from any GSM phone.
To unlock you need to insert chip with your sim card, dial 112, once it connects hang up, toggle Airport mode on and off - that's it, you unlocked your iPhone 4. We do not know yet if this is completely legal solution, so you might want to wait for DevTeam software unlock.
Here are couple screenshots from redmondpie, showing iPhone 4 unlocked using Gevey SIM on 2.10.04 baseband, running on T-Mobile US network.
And here are two videos, proving it is real: