Looking through the access and error logs on the server, whilst I'm connecting from both the address book app on my mac and from the iPhone, I can see the iPhone querying PROPFIND /addressbooks/__uid__/{uid of user} PROPFIND /addressbooks/__uid__/{uid of user}/ PROPFIND /addressbooks/__uid__/{uid of user} PROPFIND /addressbooks/__uid__/{uid of user}/ (with and without slashes) and then it does a PROPFIND /directory the addressbook app calls PROPFIND /directory PROPFIND /principals/users/{username} PROPFIND /addressbooks/__uid__/{uid of user}/addressbook/ which is when it successfully connects. I'm assuming that the iPhone is looking through the server in a different way in which to find the address books, or I've created an address book incorrectly on the mac and the iPhone is struggling to understand. If I find out more I'll post it, hopefully this will help someone other than me ;) c