system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Lately, I've been getting crank calls where, whether I pick up or not, the caller hangs up immediately leaving no message or insistance that I call someone else or anything. What is the purpose of telemarketing like that?
gpt
One reason an organization or entity would do that is to identify what numbers are "live". Suppose you are setting up a robo-calling operation and want to call everyone in Texas with your message. You can look up the area codes easily but if you called a random number the chances are it isn't valid. All you would get is some "This call cannot be completed as dialed" message.

So to prepare this organization would set up an auto-dialer to call every possible combination of numbers and see which ones connect. If they hear the tones from the calls that cannot connect they remove the number from their list, but if it connects to anything they hang up immediately. After they have culled the list they will start calling with a message.