Sonic is reselling AT&T fiber in most situations, but they provide their own support which is nice if you need it. If the problem is with the fiber, you are still relying on AT&T.
That said, I believe we are in San Jose, just mostly for aerial (telephone pole) locations. Below ground infra is much more expensive to serve, and historically we've focused on aerial for that reason, but I believe plans are moving forward to fill in the gaps in the areas where we already provide service with micro-trenching, so hopefully we'll be able to offer you something in the future.
If you want to contact me through my email in my profile) and are willing to accept that my crazy personal inbox situation might mean I easily miss it), I'm willing to do some closer looking with your actual info.
Specifically, aerial deployment through telephone poles is an order of magnitude cheaper than underground unless you get in when the neighborhood is being built (which AT&T and Comcast often do, and get pre-wired to each house). My understanding is that we are trying to fill in the areas between that aerial neighborhoods we initially built out where we provide service, it's just slower. If the availability form shows service for houses in your city that seem to have service delivered through telephone poles then it's possible we'll get to you in the semi-near future.
If you live in the bay area have service through a telephone pole and we can't service you, then I'm not sure what's going on. My understanding is we've covered most the bay area, but honestly that's not my department...