If you are interested in knowing about the current situation about the iPhone 4 baseband 4.11.08 and 4.12.01 unlock, then you have come to the right post.
Here, you'll be able to read about all informations about unlocking the iPhone 4 present, and the future of the unlocking scene

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Software Unlock iOS 5.1.1 Baseband 4.12.01
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 People who were able to get the iPhone 4 5.1.1 unlock should have kept their unlock activation tickets. There SAM unlock activation ticket allow you to keep your iPhone 4 unlocked. Creating a custom firmware can allow users to go to the iOS 5.1.1 and keep their device unlock and the baseband won't be upgraded. However, the iOS 5.1.1 can only be jailbroken tethered — that's why it's risky!

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Unlock iPhone 4 with Rebel Pro Micro SIM Card
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 It claimed to unlock the iPhone 4 on the basebands 4.11.08 and 4.12.01. However, it was discovered that it was a fake, and it could also have been a copy of the SAM unlock tool.

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AT&T Free Unlock
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Your contract time with AT&T needs to be over. Secondly, for those who have purchased from someone else and the customer has paid a beginning termination feeds, in that case your eligible. The most crucial is that you must be active AT&T customer. If you have iPhone purchased from eBay, Amazon or etc., You are in a hopeless situation.



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The downgrading of iPhone 4 baseband 4.11.08 / 4.12.01 requires these components:  ------------------------------------------------------------------------------------------------------------

1. Intel 36MY1EF 128MB NOR chip which costs US$67.00.
2. Infineon Baseband Chip X618 (pre-programmed) baseband 1.59.00 which costs US$88.00.
3. Worldwide standard shipping (can be tracked online and will take up to 20 days) which is free.
4. China domestic first class express shipping which is free
5. Labor charge which costs $24.00.
6. 30-days warranty.

This is going to work but the main issue the workers at beijingiphonerepair face is sourcing those rare 1.59.00 baseband chips.

Warnings

1. Only custom-made firmware should be used for upgrading while iTunes should be strictly avoided
2. The IMEI serial number change will be caused by the change of the chip so the unlocked iPhone can be activated using any hackivated custom firmware and latest ultrasn0w.
3. There will be no issue in the process of restoration to stock firmware.

We know the method is hectic. But this hardware hack to downgrade iPhone 4 baseband 4.12.01 / 4.11.08 to 01.59.00 is reliable and can allow you to unlock iPhone using ultrasn0w.


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Factory Unlock By IMEI :
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Unlock ANY ATT iPhone 4S, 4, 3Gs & 3G on iOS 5.1.1, 5.1, 5.0.1, 5.0 & 4.2.1. Yes this is Permanent and cannot be removed, EVER. It will work on any Blacklisted, Bad ESN or “Gulp” Stolen iPhone. This is by far the best unlock ever made and completely worth the 16 – 20 dollar price on eBay  Make sure you read the review before buy it  . Yes it will work on any New Baseband chip 3Gs as well so everybody is covered! No however the Sprint & Verizon 4S are not supported and the iPhone 4 CDMA is clearly not supported as well due to its lack of a sim card slot.

NOTICE!: If your iPhone is originally from Telus, Koodo, Telenor, Orange, Movistar, Rogers or O2 then you need to ebay search “Your Carrier iPhone Factory Unlock”. There is a different unlock version for that device. It will cost more though..

Troubleshooting:
If you keep being redirected to the Activation screen then simply Turn Auto Carrier Selection “Off” in the “Carrier” tab every time it appears. This will fix the problem.