David,
I have had AT&T Internet service ever since they offered it around here and I have never had but two instances of not being able to log on. One was a storm that knocked down some lines and the other was a site issue that they had fixed in about an hour.
Also one other thing no one has mentioned. Some time ago my speed slowed way down and after I ran a speed check I called a friend of mine who is their top DSL tech now and told him about it. He said I will call you back in about 10 minutes and he did and told me to run the speed test again. It was back to normal. They had changed the circuit packs in the offices and had left all of the newer ones set to the default setting which is the lowest speed. I run speed tests on my computers about once a week and if they come out with any large variance, then I will check.
Ron