You can jailbreak iOS 4.1 On iPhone 4, 3GS and iPhone 3 using PawnageTool 4.1 which is recently released by iPhone Dev Team, with this new-released jailbreak tool you are able to create custom firmware file and maintaining your current baseband (this what make PWT 4.1 different with LimeRa1n & GreenPois0n) and as the result you will be able to unclock your iPhone using Ultrasn0w.
Requirements before jailbreak your devices:
- Download iOS 4.1 firmware.
- Download iTunes 10.0.1 from this page.
- Download PwnageTool 4.1 from this link or this link.