Alright everyone, here is a really easy way to find out your iPhone’s Bootrom. Why would you need to know this? Well if you want to put iOS4 on your 3GS, you will need to make sure your phone has the older Bootrom.
- Old Bootrom – 359.3
- New Bootrom – 359.3.2
The following instructions were provided by machackpc.com and I give them full credit. Follow them on twitter@machackpc
I’ve added the Windows 7 Device Instance Path and Mac/Windows Screenshots
Windows Method
Step 1: Connect your iPhone 3GS to the Computer
Step 2: Place your iPhone 3GS in DFU mode. (Follow this link)
Step 3: Right click on My Computer
Step 4: Select Properties and then select Hardware Tab
Step 5: Now, click on Device Manager
Step 6: Now, Look for Universal Serial Bus (USB) Controller and select it
Step 7: Now, find “Apple Mobile Device USB Drive”
Step 8: Right click on it and select Properties
Step 9: Navigate to Details and select Device Instance ID or Device Instance Path for Windows 7
Step 10: Scroll through this string and eventually you will find the bootrom version (iBoot)

And this is what you should see if you’ve done it correctly, and my iPhone is running the old Bootrom v359.3
To get out of DFU Mode, you simply just need to hold the Power and Home button for 10 seconds. This will shut your iPhone off, and then hit the power button and you should see the Apple logo and it will continue to boot.
Mac Method
Step 1: Connect your iPhone 3GS to the Computer
Step 2: Place your iPhone 3GS in DFU mode. (Follow this link)
Step 3: Once your iPhone 3GS is in DFU, now click on the Apple logo on the top left corner.
Step 4: Select “About This Mac“
Step 5: Click on “More Info“
Step 6: Click on “USB” – Which is in the left side bar
Step 7: Now, look for “Apple Mobile Device (DFU Mode)” and select it
Step 8: Once you select that, in the bottom section look for “Serial Number“
Step 9: In the serial Number line, at the end of the you will notice iBoot. Which is nothing but your BootRom

To get out of DFU Mode, you simply just need to hold the Power and Home button for 10 seconds. This will shut your iPhone off, and then hit the power button and you should see the Apple logo and it will continue to boot.
Cheers!

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