How to make a click-to-call link for mobile Devices only using HTML/CSS

@media only screen and (max-device-width: 480px) {
.desktoptel {display:none;}
}

@media (min-device-width: 481px) {
.mobiletel {display:none;}
}

Alternative solution:

Just call us at
title="CLICK TO DIAL - Mobile Only">(800) 555-5555.

By doing this, not only is the visible indicator of a link disguised (via CSS - see examples from others), but if someone does hover over the link, the title will pop up and say "CLICK TO DIAL - Mobile Only". That way, not only is there a better user experience, but your client doesn't accuse you of having a broken link!