From this morning's Atlanta Business Chronicle:
It mentions that they are still in talks with Mandarin Oriental, but that regardless it will be a 5-star hotel operator. Mandarin would seem natural, since they are moving their US headquarters to an office on 10th Street. Also, it provides a few more details:
Residences: From $1 million to over $10 million
Spa: Dramatic, 3-story spa starting on the 20th floor and overlooking the Atlanta skyline
Groundbreaking: Early 2008