Missing support info - what XAMPP version and which Windows OS?
So assuming latest stable XAMPP version and Windows XP.
Apache in XAMPP is already a WAP enabled web server, so perhaps you would like to explain in more detail what you are trying to do that may be failing as I have a mobile web site that works in an 'out of the box' XAMPP Apache Server installation.
WML or XHTML are the markup languages used to create pages to be displayed in a Wireless Application Protocol (WAP) browser - most browsers can display WML and XHTML WAP web sites and Apache in XAMPP can serve WAP web sites 'out of the box' and needs no special configurations as all the WAP MIME settings are in place - C:\xampp\apache\conf\mime.types.
If you need it you can add index.wml
to the this entry in your \xampp\apache\conf\httpd.conf
DirectoryIndex index.php index.pl index.cgi index.asp index.shtml index.html index.htm index.wml\
default.php default.pl default.cgi default.asp default.shtml default.html default.htm \
home.php home.pl home.cgi home.asp home.shtml home.html home.htm
Save the file and restart Apache but make a backup copy of the httpd.conf file first before editing.