iPhone Dev-team has released RedSn0w 0.9.6b10 which brings tethered jailbreak for iOS 5.1 firmware. RedSn0w0.9.10b6 supports non-A5 devices on iOS 5.1 which are exploitable to GeoHot’s Limera1n exploit. You can download RedSn0w 0.9.10b6 for Mac and Windows from the links below.

Supported Devices:

• iPhone 4, iPhone 3GS
• iPod Touch 4G, 3G
• iPad 1

Download RedSn0w 0.9.10b6

RedSn0w 0.9.10b6 is available for both Windows and Mac OS. You can download it from the links below:

Download Redsn0w 0.9.10b6 for OS X
Download Redsn0w 0.9.10b6 for Windows
Download iOS 5.1
Download iTunes 10.6

Note:

It’s a tethered jailbreak which requires you to connect your device to your computer, every time you reboot your device, and use “Just Boot” feature in RedSn0w to boot in into jailbreak mode. If you turn on the device without using “Just Boot” feature, jailbreak apps won’t work (neither will Safari).

It’s untethered jailbreak iOS 5.1 for iPhone 3GS (old bootrom) users.

UltraSn0w unlockers MUST use RedSn0w to create Custom IPSW. and then restore using that custom firmware. AVOID STOCK FIRMWARE. UltraSn0w will be updated with iOS 5.1 support in a couple of days (no new baseband support)

From Dev-Team official Blog:

we realize that some of you non-A5 jailbreakers are itching to get to 5.1, even though there seems to be no compelling new feature there. Because of geohot’s limera1n exploit, those with devices earlier than the iPad 2 can test the 5.1 jailbreak waters if they really want to, using redsn0w 0.9.10b6.  Here’s what you need to know:

• This is a *tethered* 5.1 jailbreak for non-A5 devices.  You’ll need to use redsn0w to “Just Boot” your device every time it power cycles, otherwise jailbreak apps won’t work (neither will Safari).
• If you use ultrasn0w for your carrier unlock, be sure to use a custom IPSW to get to 5.1 first!  Don’t ever restore to a stock Apple IPSW!  Use redsn0w’s “Custom IPSW” button to create a NO_BB_* version of the 5.1 IPSW and restore to that instead of the stock one.  (That option is available only to 3GS and iPhone4-GSM owners.)  ultrasn0w itself will be updated for 5.1 in the next few days (same baseband support, not 5.1’s baseband).
• If you’re lucky enough to have an old-bootrom 3GS, this jailbreak is actually untethered (redsn0w will figure that part out automatically).
• While we were at it, we added @pod2g’s steaks4uce exploit to support MC models of the iPod touch 2G (whose last firmware was 4.2.1).  So now redsn0w will auto-detect and jailbreak both MB and MC versions of that older device.
• iBooks won’t work until a future update of redsn0w