iH8sn0w, the developer of Sn0wbreeze on his new tweet posted that he is working on Sn0wbreeze 2.2 which preserves iPhone 4 baseband. This will be a PwnageTool alternative for Windows. With this 2.2 release iPhone 4 users could update their firmware without updating the baseband.
For now there is no tool available to unlock iPhone baseband 02.10.00.
TinyUmbrella was able to do baseband preservation on iPhone 4 until iOS 4.1, but iOS 4.2.1 made it unable for TinyUmbrella. We can hope for the early release of Sn0wbreeze 2.2.
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