Cold Calling to Apply for Positions

“If you have to cold call apply for positions, what can you do to hedge your bets? Are unprompted emails to anyone beneficial? And if yes, to who? (For Software Engineering or Machine Learning positions in the US)”

If you do some research on a company website, you can likely find the right contact email addresses. It doesn't hurt to follow up via email after 2-3 weeks.

I've had people reach out to me via Linkedin after applying and I actually liked that. I could instantly put a face to a name and have another level of reference.

I would recommend that you NOT call anyone on the phone. It's a bit confrontational and asking for an answer to something that's hard to reply to. It's basically putting someone on the spot asking, "why haven't you contacted me yet?". Don't expect anything but a boiler-plate response to that.

If you do email someone or Linkedin message, don't just inquire on your status. Write 1-2 sentences to help sell your candidacy.

Who? You could reach out to whatever HR or Recruiter you find. If you want to take a little more of a risk and get creative, try and find out who you think runs that department/is the manager. You might naturally have more rapport with this person as they share some skillsets/interests with you. Don't put any pressure on this person, just state your skills and how you can help.