The problem with Sonic's DSL is that they are still dependent upon AT&T for the copper lines. I've been fighting with them for 3 weeks to get a stable DSL connection (I have their bonded service). After a tech visit everything starting working better (I think it was a config issue on the router).
But it was quite apparent that for Sonic, AT&T is a big problem. For most of their coverage area, they are still dependent upon AT&T to actually hook their customers up. And AT&T has no interest in maximizing your Sonic ADSL2+. They'd rather you buy VDSL/Uverse from them. I think this is what drove Sonic to start working in Fiber. Not only was it the only way to get gigabit speeds, but it was the best way for them to take control of their own destiny. When you own the fiber, you can make your customers happy. When you rely on AT&T for the copper lines, you are limited in what you can do.
(For the record, I'm in Redwood City and getting ~12Mbps down with 2 bonded lines from Sonic).