Appmodo claims to have spoken to a "reputable" AT&T employee, who told them that both MMS and tethering are coming in September. MMS will be no extra charge, but Appmodo says that tethering is going to be $55/month on top of your current data plan. Ouch. Let's hope Appmodo is right about the timing — but wrong about the price.

tethering
Tethering has just fell off my to do list if it is going for 55 a pop.I am already shelling out 70 per month and most hotels have wifi. Who needs it,
Brooksoes
Tethering Cost
Tethering is a great feature and would eliminate the need to carry an ATT Laptop Data Card. However ATT needs to re-think $55 on top of current cost unless they are trying to discourage tethering. Perhaps ATT's already over loaded 3G network doesn't need the extra traffic, so discourage participation by higher than applicable cost.
Good point
Yes, I think you've nailed it. Their network isn't yet robust enough to handle the additional traffic -- but they're working hard on it. This way they can gradually roll it out, work out the bugs and fine tune it, and at the same time appeasing those who are ready to fork over the money. As their capacity expands, seems as if they'll likely lower the price.
It seems that AT&T wants to
It seems that AT&T wants to keep people off of their data network. Of the top 3 carriers, AT&T is the only one that does NOT offer the new MiFi wiresless hotspot devices, has taken last place on offering a femtocell product and has limited the data plans for tethering from unlimited to tiered plans.
Honestly, the iPhone is not a great platform for tethering anyway and that goes for the few phones that do as well. A dedicated USB style air-card is still the best method for Internet on the go. Those devices have no overhead and are designed to go full speed on data unlike their cell phone bretheren.
By charging $55 for iPhone tethering and $60 for a regular data plan, AT&T is trying to tell us something here very quietly I think. But I do dispute the claim that the $55 charge is on top of the $30 data plan. Even AT&T would not try to sell that bogus plan in the face of its competitors.
Excellent
Thanks, Steve, for your insights.