I've been getting way more calls lately than I ever have, most of the numbers follow a sequence: 2390, 2391, etc.
I answered his one to see how it would play out.
I answered but said nothing, it began "Hi, I'm Josh, a medical alert specia...", the automated voice went silent & disconnected from that end.

It's waiting for sound, at which point it will ask, " can you hear me?" Hoping you'll answer 'yes' & then they use it for ID theft.