I don't have any inside knowledge about when or if Yahoo plans to discontinue the old 25/110 servers. They work now, but might not in the future.
Some people have just switched back to the old servers when these email problems started and the email works on the old servers, but there are also reports here at DSLR that indicate that the old servers are also having their share of access problems so this isn't something restricted to the new servers.
As I indicated earlier I couldn't even get onto the SSL server at all. So switching to the old (non-SSL) servers have at least gotten me on. I will wait to hear if/when the SSL server is back on line and also try the SSL settings every once in a while to see if they are up again. It would really be nice if ATT could let us know (not by email!) when the problem has been fixed. Tech support can't help. I once played with them for four days of no connection to the internet only to find that the whole area had been out; but tech support didn't know about it. And I don't know of any "status page" that would let me know about problems. The only one I found says that email is working normally. So it is up to the individual to fight his own battles.
I suspect that these problems are caused by Yahoo and not AT&T. Of course, AT&T is responsible because they chose Yahoo as a partner to manage the email service and apparently renewed the partnership this past spring.
For anyone that cares my SSL email is up again. And it seems like it is working more quickly than it did before it went down. Perhaps ATT/Yahoo has fixed the problem.