Spam filtering

Spam filtering covers what carriers and phone makers do to stop unwanted calls: "likely spam" labeling, direct blocking, community reporting. In the US, the STIR/SHAKEN framework authenticates the origin of VoIP numbers to detect fake caller IDs; caller-ID apps complete the setup. SMS filtering follows the same logic, with A2P routing rules.

The dark side for an honest business: the filter doesn't always tell the tradesperson from the fraudster. A number emitting many short unanswered calls, unregistered A2P traffic, a fresh number with no history — any of it can get your professional line labeled "spam," and your callbacks sent to the trash. Prevention is well known: register your A2P traffic, keep a consistent caller ID, avoid unsolicited mass campaigns.