I cold call for a living. By cold calling I mean 40 outbound calls and 15 emails or LinkedIn InMails on a regular outreach day.
Result: 6 figure income on a 70k base, for 4 years.
I also do Customer Development-type emails for my own side business, and for others (as-a-service).
Summary: it works. If you learn how to do it right.
Top tools: Stephan Schiffman's Telesales and Basho Email System.
Also: for cold calling to work you must have something of value, that solves a real pain/problem. Not something ephemeral like an app that, say, splits the dinner bill amongst friends.