LDAP, Directory Server & E-mail Address Book

I'm trying to set up the OS/400 Directory Server (V4R5) and trying to
get all of the properties to show up in Mozilla's address book.

What works:
E-mail address, First & Last names, work phone, fax, department,
work city, work postal code

The other entries don't appear to show up.  For example, if I
add to my LDIF file:

mobile: 123-456-7890

I expect it to show that phone number under "Cell Phone" in Mozilla,
but it doesn't.

Does anyone know what I'm doing wrong?  Or can anyone point me to
documentation that explains how to extend the schema on the OS/400
directory server to support the additional attributes?  (or maybe add
aliases?)

I've looked at the "LDAP Cookbook" as well as the info center, and
frankly, IBM's documentation leaves a lot to be desired.

I've found tons of good docs on doing this on a Unix machine with
OpenLDAP, and I may yet end up going that route, but I'd sure like to
get it running on OS/400...

Thanks!