Ive been totally frustrated thus far w/ my kfire. I could not get my barnacle or wifi tethering apps to show up on my fire until today by going into the apps settings and changing the options to DroidX(cdma). My fire finally picked it up in the wireless networks screen and continued to connect and was then greeted by this screen.
Asking to sign into a verizon mobile hot spot account. Im now totally dissapointed and now im thinking of getting rid of the fire as it will be totally useless to me if i cannot tether via my DroidX and or my Charge.
You need to be on a 2nd-init ROM to use wireless tether without any hacks. Otherwise, if you're on 602 or 605 rooted (any non 2nd-init ROM... i.e. senseimod), you need to flash the wugfresh tether patch.
I could tether from my DX using the patch on stock 602 rooted, and senseimod 602. I'm on SSX2.2 now though, and it doesn't need the patch. It's blur free.
I don't know anything about the Charge, I don't have one. Hope that was helpful.
EDIT: just wanted to add that my kindle fire has no problems connecting over wifi via my DX. Downloaded four games last night.