iPhone 3.0 Tethering Not Working
I have had tethering working with the iPhone betas (I'm in the developer program), but now that I have the GM version of the OS installed, I don't have the option to tether. It just doesn't show up.
My theory on what's happened is that the iPhone betas didn't use the carrier settings file (which identifies your carrier to the phone - things like the carrier name to put at the top of the phone or the default choices for the Stocks app) but now that it's started using it, my old carrier settings don't have the setting to allow tethering.
If you go into Settings / General / Network and don't see the Tethering option, check Settings / About and look at the "Carrier" line. Mine says "Rogers 4.0", and a friend's phone, which does have tethering workin, says "Rogers 4.1".
For some reason, iTunes isn't noticing that my carrier settings are out of date. It may be as simple as acquiring an updated carrier settings file, and I'm trying to locate one - I'll update this post with the results.
Update: So you need two things. The updated carrier settings, which I've attached rogers_caipcc (Download and then rename to "Rogers_ca.ipcc"), and you need to set iTunes to allow you to use them. There's information on how to do that here.