downgrading unlocked iphone 3G on 4.0.1?

[Mickey87]

Hello all! Although this is my first post I have been a frequent browser of these boards for months, and you all offer great information. Before I posted this thread I searched and searched the forums to see if there was a similar question previously answered and either I'm ignorant to the jargon or I just couldn't find the exact same scenario I'm in. So let me lay it out for you and any help or a point in the right direction will be greatly appreciated.

For Christmas my brother gave me his old unlocked 3G iPhone as I had mine stolen a few months back. It is operating on version 4.0.1 and I'm getting annoyed with how slow it is to load apps and do simple tasks. I read that this is a common problem for many 3G users using 4.0 so I'm interested in downgrading back to the 3.1.2 or 3.1.3 my old phone had and worked perfectly fine for what I needed.

Now I've never unlocked or jail broke an iPhone before so the thought of me doing it and seriously messing up makes me nervous. I found the excellent tutorial http://modmyi.com/forums/general/737...g-3gs-4-a.html posted by i.Annie and was wondering if I can use that step by step to downgrade my already unlocked iphone and have it still work for me on t-mobile or do I have to start from scratch in order to downgrade? Whatever is the most foolproof tutorial works best for me. The phone is operating on firmware 05.13.04 and I have itunes 10 operating on windows Vista. I wanted to post the question before I took the leap and locked myself out of the phone. Thank you!

Joe

[iYeow]

As long as you downgrade to any 3.xx firmware, you will not be locked out.