A useful new feature in HTML 5 is the tel: prefix that you can add before the href value of a link:
<a href="tel:8002221111"> Click here to call us now at 1-800-222-1111.</a>
Similarly to the mailto: prefix that launches an email client when clicked in a desktop browser, the tel: prefix initiates a phone call when the link in clicked in a smartphone browser.
Using the onlick handler within the link, you can insert event tracking code:
<a href="tel:8002221111" onclick="_gaq.push(['_trackEvent', 'Mobile', 'Click to Call'])">Click here to call us now at 1-800-222-1111.</a>