That’s not running a WAP site, it’s posting to your normal WP site with a mobile phone. That can be done much easier by some post-by-email plugin since many mobile phones have email on board.
Running a WAP site with WP would require templates in WML format, being served with content-type: text/vnd.wap.wml
I’m not sure such a plugin exists. Would be cool though.
Oops the plugin I linked does actually do the post by email thing, my bad… But the original site does do WAP properly so contact the admin of that site to see how they do it.