Comcast/Xfinity, of all companies, actually has a reasonably good, network-based capability, "Spam Blocker": <https://www.xfinity.com/support/articles/spam-blocker-overvi...>

I discussed it yesterday in another thread:

<https://news.ycombinator.com/item?id=49126133>

I suspect that the relevant factor is that Comcast doesn't provide significant outbound business telephony relative to its household business, though that is one of their business offerings, see: <https://business.comcast.com/>.

(I may be entirely wrong on this, I'm just learning much of this in the past few days/weeks.)