Who really stands a chance in AT&T review?

Perusing the stories about the just-revealed AT&T media review, it's a little odd to ponder the rather disparate roster of incumbents that are said to be pitching the chance to win the consolidated, really big account: Digitas, GSD&M, Initiative, Mediaedge:cia and OMD. Now really, is any client going to give this business to GSD&M or Digitas without a little help from their holding company friends? Of course not. So GSD&M will partner with OMD and Digitas will partner with Starcom or Mediavest, depending on such issues as client conflicts, and then maybe this thing can be a full-on, all-agency-holding-companies-on-deck review full of the rumors and rampant speculation which are the only things that make these reviews interesting. And if I'm wrong, I'll write a post about how screwed up my speculation is. (BTW, Adverganza is not a place where you'll see billings figures, because they are such an antiquated, inaccurate way to express what's really at stake here in terms of revenue. If someone wants to throw me a few ideas on what a reasonable average ratio of billings-to-revenue is for a media review, I'll concoct my own formula for the size of this account.)