Acknowledging the delay, AT&T said "it was important to give our customers a positive experience from day one." The carrier simply needed extra time to ensure that its network could handle a large amount of MMS traffic. The update will be pushed to 3G and 3GS owners in the way of a software update.
Unfortunately, tethering won't be making an appearance on the 25. Although AT&T expects to offer tethering in the future, they again cited a lack of network readiness. The feature could cause a traffic surge that their network simply isn't equipped to cope with yet.