Am not sure you can use itunes to find firmware and base-band version of an iPhone.
Official firmwares are firmwares from Apple and custom firmwares are customized using snowbreeze or other programs to add apps and also activate firmware.
Activation is done using original sim that came with phone.. non activated i Phone's have the iPhone logo on it and menu does not appear. There are other sims on the market now that can be used .. like Onesim to activate iPhone.
When using spirit for jailbrake then you will need to have the Iphone activated first. But with Snowbreeze,you can creat you own custom firmware which is already activated and use itunes to update your iphone with it.
So jailbreak is a way to allow the Iphone to accept apps and also be able to unlock it. And like i said there are lots of software's you can use for jailbreak. I guess you can also use the search button if you need more info.
