I also have sbc dsl and i experienced the same problem when i was initially set up a couple years back. When I was initially set up, I had no problems connecting and when I was connected the the speed was awesome. BUT, at least once every couple of hours, the connection would drop and then after my set 30 sec delay, it would reconnect w/ no issues. I called tech support to find out what was going on, they referred me to ASI. ASI did some testing and found that there was a bridgetap on my line which was causing "inconsitancies" and referred me back to sbc to have this problem fixed. I went round and round with this for about a month trying to get one or the other to take resposibility and fix it, but sbc said it was ASI's fault and ASI said it was sbc's fault. I finally ended up at sbc corporate and they said it was in fact their problem and dispatched a repair team to fix the problem. About two days later I got a call saying the bridgetap had been removed and I never experienced any other problems w/ dropped connections (besides the occassional drop due to server problems and whatnot).
As a sidenote, corporate also credited my account for 6 months worth of service to make up for all the time I wasted trying to have it fixed.