The easiest way to serve WML contents is to use any good HTTP server. I recommend Apache. If you want dynamic contents, I also recommend a server side script language called PHP. Both are of course written to serve HTTP compatible, HTML browsers, but work fairly good for WAP compatible WML micro brosers too.
  
Unless you link your WAP site with the portal of a mobile phone network provider, users have to type in the URL to your site on their phone which can be a complicated task. As "www" has become the standard hostname for HTTP server, "wap" seems to be the standard when it comes to servers containing WAP applications. Ie. "wap.domain.com".
 
One very important thing is that you remember to tell the HTTP server to tell the WML browser that it is receiving WML pages, and not HTML pages. This is done by using MIME.