Put your iPhone into DFU mode.
Then go to Start -> Control Panel -> System -> Hardware -> Device Manager on your computer.
Look for 'Universal Serial Bus (USB) Controller', you'll find
Apple Mobile Device USB Driver as a subitem there.
Right Click -choose Properties, go to Details tab, select
Device Instance Path from the dropdown box. At the end of this info string you will find the bootrom version, e.g. iBoot-359.x |