I'm Using an iPhone 4. Currently its running iOS 4.3.5 with baseband 04.10.01. And i'm Using a Gevey Sim to unlock. I need to Update my iPhone to iOS 5.1 (or 5.0.1). But i need to preserve my baseband. (because of the Gevey Sim) How can I do it?

(at this moment there is no any Jailbreak available for iPhone 4 iOS 5.1 Baseband Preserve. because of that only I need to update my iOS. I'm planing to jailbreak when it release)