If you update to official 5.0 or 5.0.1 your gevey will be useless and you will have no way of unlocking it any longer.
This is so untrue. Right now I am using an iPhone 4 with gevey sim. I have upgraded to 5.0 with snowbreeze. Snowbreeze preserves your baseband and you have the option to jailbreak (tethered) or not. There is even a way to upgrade to 5.0.1 but then you won't have the option to jailbreak. Even though you can get the gevey sim cheaper on eBay you take a chance with it. The website Applenberry is the place to order from. Then you know you have the right one. It is thirty dollars on this website.