Guest blogging purely for inbound links is a flawed strategy because the value of those links are going down. However, guest blogging for traffic is still an incredibly viable strategy. While that inbound link you get at the end of a guest post doesn’t have as much SEO value as it used to, it still has the value of exposing your content to a new audience.
Good question, for most directories I use they ask for mobile number to send a message of verification, for the ones which phone you for verification inform the company before hand to tell their customer service people to be ready. I know the bigger the company the more tricky these things get you just have to find out what works best to answer the calls even if they give you a direct number to use.