mod_ldap is a plugin for the directory interface abstraction.
Basically the directory interface is a clone of the ldap api but
can have pluggable modules to use other means such as sql of providing the data.  The only thing that uses this interface is

mod_dialplan_directory which is an example dialplan that uses
the directory interface.

This may start to sound confusing so keep in mind the ldap
api is called the "directory interface".

There is also the "xml directory" which is a section of
the FreeSWITCH virtual meta xml config registry. This is
where the domains and users are kept.

To use ldap for this a module similar to mod_xml_curl would have to be made called mod_xml_directory that would allow the "directory interface" to generate xml when the "xml directory was queried"

Basically, you would create a blank xml object then using
the param strings passed to you make an ldap query via the
directory interface that matches what is being looked for.
then as you get results you take the data and create tags into
the xml object until it's fully populated and return the object to
the caller.

If this seems like too much, you can also use mod_xml_curl to do
a CGI request to your web server then take the params and do the ldap conversion from there and send back a text representation of the xml.