Unlocking Problem

Hi, can somebody help me with my problem?

I have an iPhone 3GS with firmware 05.15.04 (version 4.2.1), and I jailbroke it with the new PwnageTool 4.2 today. The firmware number didn't change, but I didn't think anything of it since the update said it wouldn't. I then downloaded ultrasn0w, but I don't think I unlocked the phone because it won't recognize my T-Mobile SIM card. I'm confused as to what to do now… Do I have to change the baseband in order for ultrasn0w to work (to 06.15.00, for example)?

Oh, and I don't know if this means anything, but when I plugged in my iPhone to my computer after jailbreaking it but before downloading ultrasn0w, I accidentally hit Restore from last night's backup. I didn't think anything of that either because Cydia was still installed on the phone.

Sorry if this is a really obvious question. I don't know anything about this sort of thing...

05.15.04 is not unlockable via utlrasn0w (or any other way) at this time. You're pretty much screwed. You're only option is to change your baseband to 06.15.00. Just make sure you understand the consequences as outlined in the second article found on the Dev-Team Blog

If you can hold out for a few weeks, ultrasn0w will most likely be updated to unlock 05.15.04 once Apple's 4.3 firmware is released, which may be as early as the end of the month. But there's no way the Dev Team will release the update prior to the new firmware.