I noticed one strange thing recently. Every telemarketing call starts with an particular sound that resembles a modulated data block. It's very short, about 250 ms, but very audible. I'm a little curious what it is. Is it possible to capture and decode?
The regular calls are not preceded by this block, so I'm certain that it's something that telemarketers mix in. But to what purpose?
UPDATE: Someone shared this post on Hacker News. I'm happy to report they didn't conclude that I'm making shit up, but the best the hive-mind came up with was that the Caller-ID is getting sent even after the receiver is picked up. I really should record this somehow.