My BB pearl did not work reliably for tethering with 4.2 on the 8100. The tablet (both 800 and 810) could connect to the phone but actually getting data loaded from the internet was hit or more often miss. I could get a web to load if I hit reload often enough.

Once I upgraded the 8100 to 4.5 tethering on 800 and 810 with chinook worked just fine and was very stable.

I am now on a 8310 (4.5 OS) on T-MO with Diablo on both my 800 and 810 and tethering is still working just fine.

finally get N810 tether to BB 8800 working after upgrading BB 8800 to the latest 4.5 firmware, thanks rone and dubiousmike