Currently it is difficult to find out whether your iPhone 3GS or iPod Touch can be tethered. f0recast is a new tool by iH8sn0w (currently in development stage) that facilitates users to identify if their iPhone or iPod Touch can be Jailbroken or Unlocked using tethered or un-tethered method.
In order to know or find out if your iphone firmware can be jailbreaked or not, just connect your iPhone or iTouch to your computer, launch the app and push a button. It will help a lot of people who directly restore their iPhones or iPod touches without knowing that their iDevice cannot be jailbroken or unlocked.
According to iH8sn0w on twitter, f0recast tool is in its final development stages, will be released soon for download.
Note – F0recast does NOT jailbreak your device, rather tell you if your iDevice can be unlocked or Jailbroken.