Some is and some is not.
Android jailbreak
You can use free software like Greenpois0n, Redsn0w, and Lydia.
you can jailbreak any software
Updating the iPod Touch software erases the jailbreak. You can update, but it will erase your jailbreak.
If its on 3.1.3 then use "Spirit" to jailbreak it
You need to download redsn0w which lets you jailbreak on 5.0.1 software.
yes you can you use green poison rc6 for untethered jailbreak.
The reason behind the jailbreak is sometimes theft of software (PS3 Games) and that is illegal.
Ziphone, google it :)
Spirit, blackra1n, or redsn0w
go to google.com and type in Spirit jailbreak and its the first link and yes its for free
download them from loads of sites as usual, you dont need to jailbreak just to get free music