which is the best option?

[chaminade0408]

I'll make it short and simple:

currently have:
iPhone 4
baseband 03.10.01
4.2.1

I just got back from Tokyo and want to unlock my phone for use in America (t-mobile)

should I upgrade to 4.3, or unlock 4.2.1? which is easier/more likely to work?

I just tried with PwnageTool and it didn't work. It said, "The iPhone "iPhone" couldn't be restored. This device isn't eligible for the requested build."

I can't figure out what my baseband becomes if I upgrade to 4.3, so I don't know how to search for answers.

Thanks in advanced for the help!!

[i.Annie]

You can't unlock the device whether on 4.2.1 or 4.3.

You can jailbreak it now on 4.2.1 with greenpois0n though, but no unlock.

[chaminade0408]

oh really? well, is downgrading an option?

[i.Annie]

Basebands cannot be downgraded, unfortunately.