Not thrilled with the idea of people getting stranded without a working iPhone if they use the current, tethered, iOS 5 Jailbreak, Big Boss has come up with an intermediary solution -- and iOS 5 semi-tethered Jailbreak.
The semi-tethered jailbreak will allow you to reboot on the road, but with limited functionality. It is enough that you are no longer stranded, and you can use your phone, text, and many other features. This is just until you get home and can use redsn0w again to “just boot tethered”. Once you do that, you’re back to fully functional state.
Or as Miracle Max might put it: "It just so happens your Jailbreak here is only semi-tethered. There's a big difference between semi-tethered and all-tethered. Semi-tethered is slightly untethered. Now all-tethered, well with all-tethered there's usually only one thing you can do -- Go through your clothes and look for loose dock cables."
In short, you get Phone, Messages, many of the built in apps, no Safari or Mail, but if you have App Store browsers or Gmail apps, you can use those. There are some other trade-offs as well, so hit the source link below and read carefully before deciding to pull the trigger.
"Have fun storming the kernel!"
Source: Big Boss