If this is a prelude to AT&T losing their exclusivity then it's an odd move - the standard "unlimited data" cap on Verizon is 5GB. I'm not sure why AT&T would charge more for less compared to a competitor who was about to offer an alternative for their customers.
I wonder when we'll see the famed Jobs reality distortion field try and sell us on 2GB being enough data for anyone.
This also exposes the ridiculousness of mobile data pricing - the excess charges are $10 per extra 1GB, but the base plan is $15 for 250MB? Hmm.
1) This is mostly AT&T putting a stake in the ground now to be able to charge more in the future. Yes, 98% of subscribers currently use less than 2GB of data but that won't be true in 2-3 years. Instead of increasing those 200MB/2GB limits carriers will offer additional plans and reshape/abolish existing ones to nudge people into upper tiers. As happened with minutes and SMS, you'll pay more for less as time goes on, even as the cost to carriers plummets.
2) I don't know what sort of bandwidth VOIP uses, but I bet it's a lot less attractive as an alternative to regular calling with a 2GB limit.
3) Tethering is also a lot less attractive there's a 2GB data limit. Note that extra $20 doesn't buy you any more data, it just allows you to use your existing data in a different way. That really really stinks.
4) The overage charges also stink. On the $25 plan you pay $10 for an extra GB, on the $15 you pay $15 for an extra 200MB. That's just nasty.
My feeling is ATT plans to offer ~5GB at ~$35 later. They probably don't want to announce it now since it will immediately be visible that they are charging more for less data. I foresee a rush of ipad 3G purchases from now to June7.