I think I have seen all the trailers, but I must have missed noticing Charlie at the end. Anyway, I think I have read that he will be showing up for guest appearences from time to time via flashbacks. He was a very popular character and left the show on good terms as far as I know, so I am sure we'll be seeing him from time to time.

This season ought to be really interesting with the mix of flashbacks and flashforwards. It is really a shame it had to be broken in two, would have loved to have sixteen weeks to look forward to new episodes during. Also....

*****Potential minor SPOILER below*****

Just put the SPOILER warning incase anyone doesn't know that Michael is returning, though it has been clearing announced that the actor will be returning as a full time cast member, and I think he might have been in one of the trailers.
Really looking forward to the return of Michael, but I am wondering how they are going to Handle Walt. As far as I know he has not been signed on at all, and even if he is, he is a lot older now, not sure how they'll pull it off. It is not like they can bring back Michael back without Walt.