iPhone How to go from — Locked iPhone 3GS 4.2.1 baseband 05.15.04 — to — Unlocked iOS 6 ?

[el-extranjero]

Hi.
A friend of mine gave me his old iPhone 3GS.
It is locked to a different carrier than mine and it has no valid SIM card (my friend is using it in his new phone).

It has iOS 4.2.1 installed and the baseband is 05.15.04 (week 44, new bootrom it seems).
My goal would be to get it unlocked and to have iOS 6 (or the latest possible) installed and working.

From what I have read around the web, it seems that I may have to make it go to an iPad 1 baseband 06.15.00 (which scrambles GPS and WiFi) and only then I can downgrade the baseband (this part, I guess, using redsn0w 0.9.15b3) to something more useful that gets me to an unlocked iOS 6 (unthetered) state.

— Can anyone help me on how can I do that (bear in mind the phone has no valid SIM)?

— What are the steps to do it right? Does it all can be done using redsn0w 0.9.15b3 ?

It has been quite a few months waiting for the baseband downgrade, but still couldn't find a clear answer of how to unlock and upgrade to latest "unlockable" iOS 6 (unthetered), from a locked iOS 4.2.1 3GS phone. Can anyone help me on this? Thanks.

 

[Rajani Isa]

As far as the unlock, ask your buddy to call the carrier and unlock it.

 

[TriJetHero]

Be carefull with the iPad BB, only older 3GS's can use the iPad BB, with newer models you will damage your BB/radio chip.

It depends on the date it was made, check your serial and google on it.

An unlock via the carrier is easiest and most propably the cheapest, if that is not an option you can try an online IMEI unlock via grey market, fot AT&T phone they are around $5, but prizes vary depending on carrier.

 

[el-extranjero]

As far as the unlock, ask your buddy to call the carrier and unlock it.

I'd do that if that was an option, of course.
Even though the 2-year mandatory contract has expired, since he had a company account associated with this phone, the carrier is asking for a load of money. If it was a personal account, the unlock would be free.

 

[el-extranjero]

Be carefull with the iPad BB, only older 3GS's can use the iPad BB, with newer models you will damage your BB/radio chip.
It depends on the date it was made, check your serial and google on it.
An unlock via the carrier is easiest and most propably the cheapest, if that is not an option you can try an online IMEI unlock via grey market, fot AT&T phone they are around $5, but prizes vary depending on carrier.

As I posted before, I've checked the serial and the production week is 44 (4th and 5th numbers in the serial) which, for what I've read, is in that grey area between week 40 and 45, meaning results vary.
Is this a big risk with the baseband downgrade being possible now?

The carrier is not in the US.
I always thought this IMEI unlock thing was a scam. Does these kind of things really work? Do you know one url that is not a scam?

Nevertheless, can someone explain if I have to update to iOS 6 first and then try unlocking
or
if it is a case of the unlock app (please name which) doing the baseband update than downgrade and only then the app will update the device to latest iOS 6 ?

I've searched and read a bunch of tutorials but none is specific to my problem.
Or am I missing something?
Thanks