iPhone 4 for at&t iOS 5.1 bb 04.12.01

[nyrnack]

Hi I have an iPhone 4 16 gb for at&t
I really want to use it for tmobile
Many told me it's impossible to jailbreak and unlock it
But I jailbroke it and have Cydia installed on it.
(i think it's tethered ? every time i reboot it i have to plug it into computer and go into DFU mode with redsn0w in order to use Cydia)
Anyway I'm trying to unlock it and I've tried almost everything.
I have tried downgrading bb and iOS but it's not working
I don't have any SHSH blobs and I don't know how to get them.
Someone please help me!!!

 

[PsstGreek]

There is no unlock possible.

 

[nyrnack]

but then how do other people do it?

 

[Applejuiced]

but then how do other people do it?

Other people saved their baseband from previous firmware releases.
Currently there is no unlock available for your baseband version. The baseband cannot be downgraded.
Not every iPhone can be unlocked.

 

[labman]

people also ask or check before updating firmware and basebands! 😉