Here are the instructions on how to check your iPhone bootrom version on Windows or Mac without installing any third-party programs. Your device also don't have to be jailbroken to pass this check. This tutorial will be especially useful for iPhone 3GS owners as there are two bootrom versions on that devices. You need to know your iPhone 3GS bootrom version in order to successfully perform jailbreak or unlock. Note: iBoot-359.3 is the old bootrom, iBoot-359.3.2 is the new one. Let's start with Windows instruction.

How to check your iPhone bootrom version on Windows:

Step One: Connect your iPhone to PC via USB cable. Step Two: Put the device into DFU mode. For detailed instructions on how to do that visit this page. Step Three: Go to Start menu and right click on Computer. Step Four: Select Properties from the menu. Step Five: Select Device Manager from the left menu. Step Six: Search for Universal Serial Bus Controllers and double click it to expand. Step Seven: Right click the Apple Mobile Device USB Driver and choose Properties from the menu. Step Eight: Go to Details tab. Step Nine: Choose Device Instance Path from dropdown menu. Step Ten: Navigate to the end of the field to see your bootrom version. It should begin with IBOOT.

How to check your iPhone bootrom version on Mac:

Step One: Connect your iPhone to Mac with USB cable. Step Two: Turn off your iPhone and put it into DFU mode. See Step Two above to get the instructions on how to do that. Step Three: Start iTunes. It should recognize the device in DFU mode. If not, or iTunes says you're in recovery mode, repeat steps from the instruction above. Step Four: Now navigate to the top menu of your home screen and click Go menu. Step Five: Choose Utilities within Go menu. Step Six: Choose System Profiler. Step Seven: Go to USB menu on the left side. Step Eight: Find Apple Mobile Device (DFU Mode) in the center of the screen. Step Nine: See Serial Number line below. It should show your iPhone's bootrom version. It should begin with iBoot. After finding your bootrom version - check the numbers. Again, if it's 395.3 - you're on the old bootrom and it allows you to unlock and jailbreak your iPhone 3GS with no glitches.