Disclaimer: The details below involves jailbreaking in action and we strongly OPPOSE this and DO NOT support the cracking of App Store applications.

I had been learning objective C for a few weeks and even bought the iPhone development program to test out my application on the device and tried all kinds of legal updates pushed to me via Apple but the latest iPhone OS 4.0 Beta had cause lot’s of headaches to my iPhone 3G.

If you are a developer & had paid for the iPhone Development Program, go to Apple Development Portal now you can see that they had a link to download iPhone OS 4.0 Beta for 3Gs & 3G.

Naturally being an inquisitive developer and wanted to know every detail of the new OS for testing, I downloaded the 3G version of the iPhone OS 4.0.

I seriously had forgotten the phrase “Curiosity Kills The Cat”

I faced a couple of problems firstly, iPhone 3G DO NOT HAVE most of the iPhone OS 4.0 features such as multitasking and etc (Due to agreement to the developer program I cannot reveal what does not work for now) and the issue of insufficient memory crops up EVERY FEW Minutes especially playing games such as “WE RULE” and half my apps do not work.

So, the quest to downgrade my iPhone OS to 3.1.3 started.

First, I encounter missing download from apple for the legal copy of OS 3.1.3 and only left with OS 3.2 (iPad) and OS 4.0 available for download but google found me a variety of download sources of iPhone 3G version of OS 3.1.3.

One link I found is from http://www.redmondpie.com

I downloaded the OS 3.1.3 for 3G and proceed to restore from iTunes by pressing OPTION + Restore button on iTunes

Happily I went for a bath and came back and to my horror, it stuck at an error code 1015!! >_<

Then google came back with a solution of using “BlackRa1n” the jailbreak option…but wasn’t BlackRa1n not ready for 3.1.3?

Hmmm Without much consideration & out of desperation I tried downloading it from www.blackra1n.com (mac version) and clicking the “Make it rain”

My iPhone 3G screen went black and the Blackra1n app seems to be telling me that once the iPhone reboot it should be OK!

I waited seems like eternity and gave up and pressed the HOME + POWER button to shut down and POWER Button the boot back up.

Then my iTunes detected my iPhone and MIRACULOUSLY my iPhone 3G Slide to unlock screen APPEARED! WOOHOO!

I slide to unlock my iPhone 3G and find all my apps disappeared and with more digging found out the 3.1.3 is installed properly.

From the iTunes, it shows normal detection and I managed to initiate my syncing of data by pressing the “Sync” button.

Step By Step Instruction

1. Download iPhone OS 3.1.3 for your device here
2. Option + click Restore Button on iTunes
3. Browse & select the iPhone OS 3.1.3
4. Restore and encounter error code 1015
5. Download Blackra1n application (mac) here
6. Click on Blackra1n & click “Make it rain”
7. Your iPhone will black screen for some time, ignore it & Press and Hold HOME + POWER button on your iPhone
8. Press your Power button to turn it back on
9. Force quit Blackra1n application
10. iTunes will detect your iPhone as normal don’t panic wait for iPhone slide to open bar to appear
11. Do not restore from back up but click the “Sync” button on iTunes instead
12. Wait for all your data, applications, music & etc to transfer over (Takes a LONG TIME)
13. When syncing is completed, unplug the cable and watch your iPhone reboot to apple logo and back to slide to unlock screen!
14. Your iPhone 3G successfully downgraded from OS 4.0 to OS 3.1.3

Disclaimer Warning: Do the above only when really necessary & I am not responsible for any damage & loss of property or lives in any event you chose to follow my desperate measures written above. However, when times like this we all need is some help and hopefully the above can help you.

Note: I am not sure if your iPhone are jailbroken after the steps above so use it at your own risk

UPDATE: I am not sure if Spirit Jailbreak can essentially do the same or not…but anyone successfully downgrade to 3.1.3 from 4.0 do share your story.

NOTE: Do note that the above are done with iTunes 9.1.1 hence not sure what’s the different with the latest iTunes 9.2

You can download iTunes 9.1.1 (Mac) (Window 32bit / 64bit) & downgrade iTunes instructions.

UPDATE: The above procedure is outdated to 3G with iOS 4.0 with old iTunes version. However kudos to CNET they found another way similar to downgrade to 3.1.3 with new iTunes. (Kudos to lifehacker too)

Download Recboot here.

(Note: personally I haven’t tried it yet so anyone with success please do comment)