Why bother? I've used my San Francisco teathered a few times now and nothing has been said. I'll add that I limited my data usage though as 500mb a month doesn't go all that far.
I Think the "Personal Hotspot" tool is the only reason im looking Forward to iOS 4.3, Hopefully its Free...
To Tether you have to purchase a Bolt-on for like £15 p/m for like 2gb usage.
Just Wait for 4.3 and see what happens...
You get unlimited data for mobile phone usage, it's pretty simple really.