Here is a fun SEO question I found the other day where Google's John Mueller if Google passes PageRank to mailto or telephone hyperlinks. The answer is no, Google only follows links between canonical URLs and in mailto and tel links, there is no real canonical set.
Here is the Q&A on Twitter:
We see links as being between canonical URLs, so if the href points to something that's not a canonical URL for our indexing, then we don't see that as a link. Seems like a neat Gedankenexperiment though -- pagerank in phone numbers? Hmm :)
— 🍌 John 🍌 (@JohnMu) February 24, 2021
Here is a mailto HTML link which triggers your email client to open and send an email to this email address:
Here is a telephone HTML link which triggers your phone or your computer's calling program to dial this phone number:
Why would you want to pass Google PageRank to those locations is something I do not understand but the question is new.
Forum discussion at Twitter.