Sorely being tested by robo spam callers hitting my oncall line.
That happened just once at an ISP I worked at. It was a slow day, and we needed to bleed off some stress. Since these people were obviously harassing us with illegal calls, we decided to flood their phone switch with legit calls. We hit them with every line we had, every call center staffer, every NOC from across the US. Nonstop until their scummy CEO called and threatened us. Then we did it some more until he apologized.