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What is iPhone Baseband, Sim Lock and Jailbreak?

Alfred is a long-time teacher and computer enthusiast who works with and troubleshoots a wide range of computing devices.

When you opt to jailbreak your iPhone it is important to understand the terms closely related it, so as not to make mistakes along the way.

The following are popular terminology related to iPhone jailbreak:

  • Baseband
  • Sim Lock
  • Jailbreak

1. iPhone Baseband

The iPhone Baseband is a combination of modem hardware chip and a special low-level software called firmware. The hardware device is responsible for all cellular activities that require the antenna. The firmware is identified with figures such as 04.12.01 and 04.10.01.

On the other hand, Wi-Fi and Bluetooth hardware are managed by the iPhone processor, though the baseband firmware stores their MAC addresses.

The Qualcom baseband modem chip in iPhone 5

The Qualcom baseband modem chip in iPhone 5

2. iPhone Sim Lock Status

This refers to the status of the iPhone when first purchased in relation to a cellular network.

The iPhone basically sells in two states:

  • iPhone locked to carrier network
  • Factory Unlocked iPhone.

A locked one means that it can only function with a sim card provided by the retailing telecom company like AT & T or Verizon in the USA. The user enters into an agreement with them to pay for the iPhone in a period of up to two years. The starting price for a new locked iPhone can be as low as $99.00.

On the other hand, a factory unlocked iPhone comes open to all network sim card around the world. The drawback is that it must be paid for at once, making it rather pricey.

Caution that an iPhone is locked to a specific carrier network

Caution that an iPhone is locked to a specific carrier network

3. iPhone Jailbreak

This is the installation of third-party modification codes onto the iPhone OS firmware to allow a user customize it to their liking. It makes it to bypass the rather stringent restrictions that come with the factory operating system.

Apple allows installation of vetted software only through iTunes. Jailbreaking, on the other hand, allows the user to install other software through Cydia, which boasts of collections of third-party tweaks and apps in its partner repositories.

Evasion is a tool that can be used to jailbreak an iPhone

Evasion is a tool that can be used to jailbreak an iPhone

Relationship Between Baseband, Jailbreak and Unlock

If you own an iPhone that is locked to a specific carrier network, you can have it factory unlocked for free or for a fee.

Usually, the carrier network from it was purchased should unlock it for free. Third party unlock services will charge a fee. Both of these services will make use of the IMEI number.

The iPhone can also get temporarily unlocked using hardware or software hacks. Hardware solutions rotate around the popular sim interposers like R-sim or Gevey Sim. Popular software unlock solution is called Ultrasn0w and it is effective in iPhone 4 and below. Software-based unlock is not supported in the latter iPhones.

If you want to unlock your carrier locked iPhone, you normally have to first jailbreak it or have it unlocked officially by your network carrier: AT&T and other online stores offer IMEI based iPhone unlock solutions with or without contract agreements.

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You can save yourself lots of headache by purchasing an unlocked iPhone from Apple stores.

In order to the old iPhones using Ultrans0w, you must jailbreak it first. And in order to do this safely, you must also know the iPhone baseband (BB) and IOS firmware status. Baseband is referred to as Modem Firmware and is identified by strings like 04.10.01. (see image below).

iPhone firmware is referred to as Version and identified with strings like 5.1 (9B176). (see image below)

Firmware and baseband version of iPhone

Firmware and baseband version of iPhone

In order to unlock an iPhone using Ultrasn0w make sure its baseband is supported.

Below is a list of some of the more popular iPhone basebands that can be unlocked via software:

  • 01.59.00
  • 02.10.04
  • 04.11.08
  • 2.0.10
  • 04.12.01

Do Not Upgrade iPhone Baseband

If you unlock your iPhone using Ultrasn0w always take care not to update to the newer firmware. New firmware installations always upgrade your baseband. This is okay if your iPhone is factory unlocked or you are still on the original network carrier. If not and you upgrade without insight, your jailbroken iPhone will lose network after the update.

To avoid this nightmare, always use your jailbreaking software to update, and always ensure you preserve the baseband in the process.Redsnow can help preserve baseband during updating and jailbreaking.

iPhone baseband upgrade in progress

iPhone baseband upgrade in progress

© 2012 Alfred Amuno


andrew on January 27, 2013:

get factory unlocks from these guys

Alfred Amuno (author) from Kampala on January 17, 2013:

Hello Aastyre. At the moment there is actually no jailbreak for IOS 6.0 and above for owners of IPhone 4S and 5. You can however opt to upgrade to the clean IOS 6.1

Read here for more info:

aastyre99 on January 17, 2013:

If i have a factory unlocked iphone 4s version 5.1.1 , and I jail breaked it, so will I be able then to update to version 6.0.1 ?

Alfred Amuno (author) from Kampala on August 30, 2012:

Sajapul, once your iPhone has been unlocked officially, you are free to do what you want with it. Your unlock status will remain whatever you do with it.

Sapajul on August 30, 2012:

I have and iphone unlocked by AT&T and i want to know if i would be encountering and issues or may lose the unlocking by doing a jailbreak.

Alfred Amuno (author) from Kampala on August 25, 2012:

It is not very easy to know that an iPhone is factory unlocked unless it is accompanied with a validating receipt.

However, a call to Apple support staff can help verify this. Of course you should have the iPhone IMEI noted down, which you will give them.

A jail broken iPhone normally has Cydia and other third party non Apple Store apps installed in it. A factory unlocked or iPhone unlocked via gevey sim only show original apps.

Hope this helps.

ritom on August 25, 2012:

hi, im interested in buying a second hand i phone 4 16 gb,how i can understand that if its factory unlocked or jail break?????

Alfred Amuno (author) from Kampala on August 16, 2012:

Hello i-Plus, sorry I did not get to you soon enough. Hope you have fixed the iPhone issue by now, if not then read the simple explanation here.

First of all the baseband you have mentioned is un-lockable via Gevey Ultra S from ApplenBerry. It will cost you over $100 and it is up to you to see if it is worth it. Check eBay for pricing and instructions. You also don’t need to jailbreak your iPhone if you do not want to.

Secondly, if you are to jailbreak your iPhone with older un-lockable basebands, always endeavor to preserve them. As always, better the devil you know than the one you don’t.

Third, when using Redsnow for whatever reason, always use Custom IPSW to preserve your baseband and when restoring in iTunes use the shift key so that you are able to select the custom IPSW you made with Redsnow.

Remember, baseband 2.0.12 is the latest BB as of now and therefore can never be updated any further. Pod2G the renowned creator of Absinthe 5.1.1 jailbreak is also working on software and free unlock solution for the new basebands.

Fourth, UnlockBoot is a new place where users are promised iPhone unlock via IMEI. The site promises to unlock anything including the stubborn iPhone BBs 4.11.08 and 4.10.1.

And finally, I hope you also know that Apple through AT & T and selected carrier networks around the world give free unlock solutions for any one that fulfills contract agreement. If you are in good books with them, this could be your best bet! It is totally legal and sanctioned by big brother himself. Read the hub below for more info:

As always, it is important to remember that the internet is full of individuals who will do anything to scam money out of you. So tread with care when buying stuff and passing your IMEI around.

Good luck.

i-plus-i on August 14, 2012:

Hello amuno,

I submitted the following questions on this hub yesterday but, somehow it dint get posted. So I'm resubmit same questions hoping that this time I might get some needed advice. Tanks again and here the questions:

Great article but been new to these sort of things, I'm still confuse on what (and how) to do to jailbreak AND unlock my iPhone 4s.

Here's the scenario: I have the iPhone 4s locked to Rogers (Canada) running the 5.1.1 firmware and the baseband 2.0.12. I need to unlock it so I can use different carriers sim cards. I would also like to jailbreak it for the obvious reasons. Now the questions:

1) If I jailbreak it, let say with Redsnow, should I preserve the baseband and then unlock it or should I let Redsnow upgrade the baseband and then unlock it.

2) If it can't be unlocked, can I jailbreak it and unlock it later when the code will be available and if so, should I preserve the baseband.

3) When running Redsnow, should I click the Extras tab and select Custom IPSW first or jailbreak it and then go to Custom IPSW.

4) About downgrading the firmware to 5.0.1, would that help.

As you can see from the questions, I'm really new and confuse on these thinks and I'm hoping that you can help me to understand and achieve my goals. Thank you so much for your time

Alfred Amuno (author) from Kampala on August 08, 2012:

Hello Nivas, it is possible to know your status only if you call Apple with your IMEI. Type *#06# in your iPhone phone app to find out your IMEI. is a website that claims to tell you more about your iPhone. If you do not fear who gets to know your IMEI then you could try them. I personally haven't used the website.

Nivas on August 06, 2012:

How to identify or confirm whether iPhone is factory unlocked?

Erik on July 21, 2012:

Is there an unlock for 1.0.13?

Alfred Amuno (author) from Kampala on July 05, 2012:

Did you mean 04.10.01? Yes, gevey sim unlocks the this baseband. 04.01.01 should be in Android family.

k.boa on July 05, 2012:

does the gevey sim unlock firmware 04.01.01

Alfred Amuno (author) from Kampala on June 30, 2012:

Thanks MB. Will always be updating the info, and i hope you join the iPhone community.

marketingbloke on June 30, 2012:

I don't own an iPhone but when I need to jailbreak one I know where to look now =]

Alfred Amuno (author) from Kampala on June 27, 2012:

You are quite right LocalGuy. You sometimes get goose bumps when something goes wrong with the updates or iTunes restore. But over time you kind of get used to the hiccups, and it becomes a pleasure walking through the process.

LocalGuy on June 27, 2012:

Having an unlocked iPhone can be such a blessing and such a curse at the same time. Mainly because you have to be more mindful when you do any updates. Thanks for the informational read.

Alfred Amuno (author) from Kampala on June 03, 2012:

@Waseem, it depends on whether you own an iPhone under contract or not. Like explained above your phone can be unlocked as soon as you complete your contract with AT&T. Alternatively, google for a site that uses your IMEI to unlock your phone. They will charge a fee and remotely use your iPhone IMEI to unlock it. In the article above is a link to one of those sites. I've never used it and don't take my word for it.

Waseem on June 03, 2012:

my Iphone modem firmware is 04.11.08, how do i unlock my iphone???

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