I used to work for a company where a vendors first unsolicited sales call would get them on our grey list. That being a list of vendors we would only consider purchasing from as an absolute last resort.

A second unsolicited sales call would result in permanent blacklisting.

Our IVR system warned callers that unsolicited sales calls would result in this action.

In the IT department alone 90% of incoming calls were sales calls. After this rule was brought in the volume was much reduced.

Also, we learned a lot of new swear words from angry salespeople.