How to Check the Bootrom Version of Your iPhone (Mac)
Here are the steps that has to be followed in-order on to determine the bootrom version of one’s iPhone while using Mac OS X.
The first step require you to connect your iPhone to the computer and put it into DFU mode.
Here, you will need the details pane, locate the Serial Number field and at the end you will see your bootrom version. It will look something like [iBoot-359.3]