Rooting isn't breaking the terms of service. Rooting is violating the 30 day warranty you get from boost along with whatever warranty that Samsung sticks on the phone.
As far as tethering goes, I think it would be pretty difficult for them to figure out that you're tethering without actually spying on your data.
I actually know a few people who's service been terminated cause of using the wifi hacks/tether with out paying for it so use at your own risk!
Upvote
0