3GS 05.12.01 - Confirming process

[3Guser2011]

Good morning everyone,
I am trying to confirm the process for my iPhone 3GS on 05.12.01 baseband, 3.1.3 firmware.
I need to keep the unlock for T-Mobile and stay on a lower baseband. I want to go to the highest possible firmware but save the most baseband (no iPad unlock, etc.). I want to jailbreak/activate and then go into Cydia to add Ultrasn0w for T-Mobile.
Should I go to 4.2.1 and preserve baseband by using a custom firmware? Which program or process should I use? I'm on PC.
Thanks for the advise!

[bondkt]

Wait. Wait for sn0wbeeze for 4.2.1, should be coming out within a week or two ( at least thats what the maker said). allows you to make custom firmwares for windows.

[qnc]

I had a 3GS on 3.1.2/05.11.07 and opted to go to 4.1 instead of 4.2.1.

I used sn0wbreeze 2.1 that was mentioned above. Cooked custom firmware. Restored no problem. I ran tiny umbrella to point iTunes to my saved shah blobs. Now running 3GS on 4.1/05.11.07 mo issues.

[3Guser2011]

I had a 3GS on 3.1.2/05.11.07 and opted to go to 4.1 instead of 4.2.1.

I used sn0wbreeze 2.1 that was mentioned above. Cooked custom firmware. Restored no problem. I ran tiny umbrella to point iTunes to my saved shah blobs. Now running 3GS on 4.1/05.11.07 mo issues.

Why rather 4.1 than 4.2.1?
How long or where can I find out about this new program to get 4.2.1? Or use custom firmware (that preserves baseband) to restore through iTunes?
Would this save my baseband and keep it unlockable through Cydia?
Thanks.

[bondkt]

because 4.1 is currently able to be made into a custom FW, where as 4.2.1 isn't (give it a week or two). the name of the app you need is sn0wbreeze (your on pc). if you make a custom FW with it it will preserve your baseband.

[3Guser2011]

because 4.1 is currently able to be made into a custom FW, where as 4.2.1 isn't (give it a week or two). the name of the app you need is sn0wbreeze (your on pc). if you make a custom FW with it it will preserve your baseband.

So... download latest Sn0wbreeze (2.1), download 4.1 firmware, make custom firmware, select baseband preserve (is this an option for 3GS 4.1 so I can keep 05.12.01?), DFU mode and restore to my new custom firmware I just created?

[bondkt]

you will have to enter pwned dfu mode but yeah...

or you could wait for the 4.2.1 version due out within a week or two.....

[qnc]

Yeah what bondkt said. Plus greenpois0n was not released yet. I would have stayed on 3.1.2, but got tired of my apps saying I needed 4.0 firmware. Plus all the cool cyrus tweaks for 4.x. Lastly I knew it would be easier to downgrade in case I wanted to.