This is a blatant advertisement for a way to collect phone numbers. I'm not sure breaching privacy and social engineering scheme are welcome or else HN would be filled with malwares and the likes.
This isn't an advertisement, it is a marketing program. they aren't advertising Breather itself, just a side-project.
As for HN and marketing programs, you may notice that Hacker News is run by Y Combinator. YC has a considerable interest in owning the news platform for startups and engineers. This is not a coincidence.
Not anymore than any other service that to work asks for phone numbers or email addresses.
You might not appreciate or have a use for the service, which is tongue in cheek, but that doesn't make it "malware" or "social engineering".