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.
Remember when you used to rely solely on search engines for traffic? Remember when you worked on SEO and lived and died by your placement in Google? Were you #1? Assured success. Well, okay, maybe not assured. Success only came if the keywords were relevant to your site users, but it was the only real roadmap to generating site traffic and revenue.