Offered tiered pricing. $5/mo for 100MB, $10/mo for 250MB, $20/mo for 1GB, $30/mo for unlimited.
As for the $30/mo unlimited, I believe part of the reason why AT&T removed the unlimited option in the first place is because a disproportional amount of bandwidth is spent by people who jailbroke their iPhone and use 100+GB/month using it as a 3G modem.
Also, you don't need to jailbreak to tether. I forget the details, but basically you go to a web address and install a new carrier profile and thats it.
If AT&T want to be the big boys on the block they have to invest in their network, end of story. The reason they got rid of the unlimited option is because they want to make all the money and not do a thing to improve their network.