There's some tutorials on iPhonulo.us:
iPhone 3G/2G: http://bit.ly/dfngOd
iPhone 3GS: http://bit.ly/cHJ6wt
iPhone 4: http://bit.ly/cANg1o
Hope this helped :)
By jailbreaking it.
Jailbreaking will void your iPhone's warranty.
You cant without jailbreaking it.
Jailbreaking is free.
Jailbreaking a phone is partially legal and partially illegal. I have a post regarding this http://www.techlucid.com/2013/11/is-jailbreaking-illegal-or-not/
Yes and it works pretty well for me
yes it is absolutely legal
It is okay to jailbreak your iPhone 3g. The only downside to jailbreaking your iPhone is that you will loose your Apple warranty.
Yes by jailbreaking your apple device
No. Sorry.
It is not illegal but will invalidate any warranty.
If you unlock it by jailbreaking it will. Jailbreaking alone does not allow you to use another carrier's SIM card in the iPhone. It has to be jailbroken and then unlocked. Once you jailbreak it then Cydia will be on the device and then you go in to Cydia and run Ultrasn0w to unlock it