I have recently installed the 3.1 beta 2 on my 3GS. I was hoping to be able to unlock my phone so that I could use it on T-Mobile, but I realized that ultrasn0w requires 3.0 and the older baseband. I have been able to downgrade to the 3.0 firmware, but the newer baseband from 3.1 still remains. Is there any way to downgrade my baseband so that I can unlock my phone for an alternate carrier? I've searched all over the Internet, but I can't seem to find anything... Any help would be appreciated. :-)

No baseband downgrader for 3.1 currently exists for the iPhone 3G or 3GS.

Sorry You're going to have to wait until the 3.1 unlock or baseband downgrader is released. Stay current with iPhone news.

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iPhone 2G T-Mobile USA
17 November 2007
1.1.1-->3.0 (jailbreakme.com, anySIM, iJailbreak, ZiPhone, PwnageTool, QuickPwn)

iPhone 3G AT&T/China Mobile
5 January 2008
2.2-->3.1 (yellow/red/ultrasn0w, PwnageTool, QuickPwn)

I can try to answer your iPhone related questions! follow me at @acwan on twitter!

bro you shoulda kept updated at blog.iphone-dev.org.... now you have to wait for some kinda downgrader so ull be out of service for awhile

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iPhone 3GS - 3.0 T-Mobile
Computers:
Dell i545s
Operating Systems:
Windows Vista
OSX Leopard (iDeneb 10.5.8)

MacBook5,2
OSX Leopard 10.5.8

It is highly unlikely that you will ever be able to downgrade the BB on the 3GS - why on earth did you upgrade?

Beta 3 is out now but if you ever intend using UltraSn0w you should NOT try it!

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He who asks a question looks foolish for 5 minutes. He who doesn't ask a question remains foolish forever.

Well.. I upgraded my 3GS to the latest 3.1 beta. I guess i'll just use my old 2G iPhone with T-Mo until an unlock comes out.

You might have a very long wait.
Using Beta software is never a good idea unless you know what you are letting yourself in for. I only ever do it when I am certain that the author will listen to, and act on, my feedback and only then if I am prepared to put up with software that might not work.
The Dev Team have warned people not to upgrade your firmware if you wand UltraSn0w to work without first checking with them first.
I hope you have your signed iBSS and iBEC otherwise you might be totally out of luck. Even with them I would not expect an unlock any time soon.

__________________
He who asks a question looks foolish for 5 minutes. He who doesn't ask a question remains foolish forever.

Confucious - I entered in my ECID number to the purplera1n website and got the certificate. I also have the iBEC and iBSS file that i got with BEC/BSS grabber. Should I be alright then for a future unlock?