Spirit is an untethered jailbreak for iPad, iPhone, and iPod touch on the latest firmwares.
Spirit is not a carrier unlock.
If you currently are using a tethered jailbreak, you have to restore to use Spirit. Do not upgrade if you use an unlock on an iPhone 3G or 3GS. (You can, however, restore to 3.1.2 if you have SHSH blobs for that version.)
Any iPad, iPhone, or iPod touch on firmware 3.1.2, 3.1.3, or 3.2.
An activated device: one not stuck on the Connect to iTunes or Emergency Call screen.
Any version of iTunes 9 (including 9.1.1).
Syncing with iTunes before trying this highly recommended.
Note: On iPad, all this is still sort of beta. Some packages in Cydia, not designed for iPad, might screw up your system and require you to restore. Be careful. (And no, Cydia's appearance is not final.)