Upgrade iPhone 3GS

[sagarpachorkar01]

Hello! I have an iPhone 3GS 32GB (Black) is currently on iPhone OS (3.1)
Model - MC137LL
Modem Firmware - 5.11.07
I'm interested in upgrading it to 4.0 without losing it's unlock. Remember, I don't have the official SIM card to activate the phone. I totally depend on the unlock to get cellular services. Please help me coz I'm confused. My device has SHSHs on 3.1.2, 3.1.3, 4.0, 4.0.1, 4.0.2
Please help me out. Your response is greatly appreciated.

P.S. - I had lost unlock due to my carelessness previously by upgrading other phone from 3.1.2 to 3.1.3

[i.Annie]

modmyi.com/guides/restore-iphone-3gs-3-1-2-using-shshs-file-cydia-windows/

Just replace 3.1.2 with 4.0

[sagarpachorkar01]

modmyi.com/guides/restore-iphone-3gs-3-1-2-using-shshs-file-cydia-windows/

Just replace 3.1.2 with 4.0

Actually I use a Mac and when I tried it, I'm stuck on the activation screen. I don't have the official SIM card (ATT).

[i.Annie]

Ok then Google the Mac version. Or go thru the Guides section here on MMi to find a Mac guide.

Youll need an official carrier's SIM card to activate to JB on iOS 4.

[Trooper Sam]

AT&T SIMs are cheap on eBay, and you'd never have to sweat it again.