If you want measure your mobile visitors that visited your website, let login to google webmaster and see how many visitors visited your website via mobile devices. It's good tool to know your mobile audiences
We use Google Analytics to track mobile visitors to our website. It gives us information on what types of devices, what pages they visited, and the path they took through our site. What it does not capture are all the SMS messages we send as part of our mobile campaigns. We track those by counting the usage of the special offers we promote with SMS and by tracking out message deliverability.