People have used exploits in the browser in the past with jailbreakme.com. However apple's really good at plugging these things, so software exploits. Specifically bootrom exploits are the only lasting way.
So I would say you do need software, although its very easy to use, the community does a brilliant job....and thanks to youtube, theres about a ten thousand 13 year old boys who'll walk you through the process.
You do. Its pretty simple to do though. I highly recommend that you do jailbreak though; it opens the iPhone up to so many more apps. You can find apps in the [snipped] market that allow you customize your iPhone and make it appear as if it were an Android, which is pretty cool!
Each version of the iPhone requires a different jailbreak.
I was just trying to jailbreak an iPhone 4 with Blackra1n but ran into a number of problems. It also is different based on the OS of the computer you are using.
There are a lot of details and it is not easy to do in a forum.
You need to Google it...
If you want to get a little bit more tricky like making themes you will have to learn some basic coding.
There is a new app that is not included with cydia sources by default you might want to check out. iSwipe it allows you to type by sliding your finger across the screen and it inserts the text. Add Wynd Repo http://wynd.x10.mx/repo It is no where near perfect, but for one guy building it, it is coming along nicely.