Updating already jailbroken Iphone 4 to IOS 5. Help!

[Prachel89]

Hi! I have an iphone 4 that is currently jailbroken and unlocked for t-mobile using a gevey sim. It is running on a modern firmware of 03.10.01 and version 4.2.1. I have been looking to upgrade to IOS 5 but i was wondering if there was any way to do so without losing my jailbreak and having to redo the jailbreak. More importantly, i must keep my phone unlocked so that i can use it with T-mobile. I'm thinking my best bet is Pwnage tool, but i'd hate to mess it up! also, if i lose my jailbreak, will by Gevey unlock stop working as well? Clearly i'm pretty uninformed about jailbreaking. Haha. Thank you!