W52P LDAP or Remote Phonebook

[Patrick9]

Hi
I have new a Yealink W52P.
But it is described in http://support.yealink.com/faq/faqInfo?id=232 that LDAP should be available, but it isn't.
I have firmware:
Base: 25.73.0.40
Handset 26.73.0.11

Nevertheless I tried to use Remote Phonebook, but I always get a "Connect Error!" message on the handset when selecting the phonebook. The xml has the following format:
<YealinkIPPhoneBook>
<Title>Yealink</Title>
<Menu Name="qwe">
<Unit Name="Patrick9" default_photo="Resource:" Phone3="+4144xxxxxxx" Phone2="+4179xxxxxxx" Phone1=""/>
</Menu>
</YealinkIPPhoneBook>

And once more:
I prefer to use LDAP and I'm surprised that this is not available as mentioned in other posts too.

Thanks
Patrick