How to use HTML to do a Skype call?

Try “callto” (with no uppercase letters).

<a href="https://stackoverflow.com/questions/3855650/callto://+***********">Link will initiate Skype to call my number!</a>

<a href="skype:********?call">Link will initiate Skype
   to call my Skype username!</a>

source: http://geek.michaelgrace.org/2010/03/create-html-link-that-starts-a-skype-call/