Looking for an addressbook (web)application that read/writes LDAP.

In an existing infra-structure based on Debian/Cyrus/Exim/Horde/LDAP I'm trying to make all the clients (OSX and Windows 7, preferably also iPhone and blackberry) work with a centralized LDAP addressbook database. Right now horde is used for webmail. For email this works fine, but I'm struggling to make a central addressbook that's readable for all clients.

I can't make Horde use the LDAP addresbook that Thunderbird uses (Authentication works fine though). The app we use to write to the LDAP database is homegrown and we need advanced features, like mailinglists. Non-geeks need to be able to use this, so I can't use barebones ldap editoprs like LDAPBrowser and LDAPphpadmin.

I've two questions :

• Does anybody have a suggestion for an addressbook application that can read and write to an LDAP addressbook so that Thunderbird and Apple Mail users can use it?
• Would it be better to rework the complete email infra-structure and use something like Zimbra?

I strongly prefer an open source solution.

From serverfault Jasper

• Really, don't think about get this going with a homegrown solution. You will experience so many problems and incompatibilities that you will go mad over it and still have no working solution.

  As an example: Both Thunderbird and Apple Mail can read LDAP address books, but neither can write them, and IIRC there are minor differences in the required schema to make interaction difficult.

  Zimbra, OpenExchange, Zarafa etc. as full grown groupware suites make all this considerable easier or possible at all with specialized connectors for all kind of applications. As a matter of fact, they did all the work necessary to get all the components play together for you, as i.e Zimbra is heavily based on open source components.

  From SvenW