I've noticed a few trends in my visitor lists. One is people looking for information about AT&T U-verse blocking port 25.
Yes they, like many ISPs are blocking out bound port 25 for non-business customers. This is in an attempt to cut down on spam. I think it's a failed attempt, because the zombies still spam like mad, but meh.
I was able to get my U-verse connection un-blocked by calling tech support. I also have a static IP address block. If you're trying to find out a way to get around the block good luck. If you have a reason that you need out bound port 25, and are not a spammer, you'll need to call Customer Support.