Apple released the Gold Master version of iOS 4.3 for iPhone 4(GSM), iPhone 3GS,iPad and iPod Touch 3G/4G.
The release is meant for developers enrolled in Apple developer program. Hence, only registered members can download iOS 4.3 GM.
Please do not update if you need unlock or jailbreak. It is already jailbroken via custom PawnageTool bundle but is only meant for advanced users.
Download: iOS 4.3 GM