Can I do that with phone numbers? Building apps to successfully use phone numbers worldwide

As a developer, what can and can’t you do with Phone Numbers to keep you and you app legit across dozens and even hundreds of countries? Learn the best practices of using phone numbers in your apps for voice and messaging with users and customers to defeat bad actors, avoid common fatal flaws, and stay good with pesky national regulations.
Patrick Loomis, Ike DeLorenzo