[From Hans] Hans caught this via the Gizmodo and it seems Dev Team's UltraSn0w unlock works with an iPhone 3GS that's been jailbroken via purplera1n with mixed success. "Good times! It looks like Dev Team's UltraSn0w unlock works with an iPhone 3GS that's been jailbroken via purplera1n. But be warned: Some users are reporting mixed success.
On Friday, George Hotz (aka the guy who unlocked the original iPhone 2G) released his purplera1n iPhone 3GS jailbreak tool." Read in full.