This is a quas-B.S. report. ATT may have lost its exclusivity but, if so, ATT has no idea when Apple will announce it. It won't be on Wed. Here is why:
Apple has said it's traditional iPhone launch period is June/July. We all know Apple is set in its ways on these kind of things. It makes no financial sense to make a Verizon 3GS CDMA phone or a T-Mobile 3GS compatible w/ their 3G data. And Apple is not going release a whole new iPhone which would either absorb the new tablet's excitement, or be overlooked because everyone is focusing on the tablet.
If Apple were to announce "coming to [insert carrier]" in June then that would delay sales of a lot of iPhones from people who would rather wait that contract w/ ATT. Apple's style is to hold announcement until the last minute to spare as much sale damage as possible.
So logically the time for Apple to make this announcement is at the next iPhone hardware event, say May or early June.