On those Windows machines with Skype installed, it tends to convert all phone-formatted numbers to Skype links so you can click it in order to make a call on Skype.
Skype has taken to adding a randomly generated string of numbers to the end of their span tag, so the above response from Groo is not entirely accurate anymore. To correctly select all Skype tags on a page, use CSS3 wildcard selectors like such :
span[class^='skype_pnh_container'] {display:none !important;}
span[class^='skype_pnh_print_container'] {display:inline !important;}
the ^=
operator causes an attribute selector to mach elements that have an class containing a value that STARTS WITH 'skype_pnh_container' and 'skype_pnh_print_container'