Tethering disappeared on 4.2 update wATT iPhone 3G

I have a 32G iPhone 3GS and have been using tethering with AT&T. I was on 4.0 and then upgraded to 4.1 and on to 4.2 last week when 4.2 was released. Now tethering is no longer available on the Network settings screen? What happened? I see a similar issue for 3G users, but I have a 3GS.
I reset the network settings and have re-booted with no luck. Any ideas? I was going to use the tethering in a presentation on Monday. How can I be sure the carrier settings are up to date?
MacBook 2 GHZ iMac, iPhones, iPods....