I am struggling with the same issue. I think I found the answer, but I have not yet tested it.
My setup is a mini server connected to a Time Capsule to connect to the internet. Time Capsule is set up to let Contacts and Calendar information.
My domain name is updated through a DNS service.
If your domain name is registered for DNS as domain.com (A Record), you may need to add a new hostname to your DNS service, creating a new A record, server.domain.com.
From what I read, this is the most likely issue with the problem you have described. I have been struggling with this for the past few days. I just need to get outside my wifi coverage to see if adding the new A record has fixed it.
Hope this helps.
I have had a look at my dns hosting at no-ip.com. It doesn´t look like i can add another A record (or even change it). I was hoping to find a way to change the dns configuration on my home server to accomplish this?
It would be interesting to know if adding the A record resolves your issue though.....
I can provide an update.
Adding the A record server.domain.com to my DNS service did solve the issue.
I added the new A record: Add Hostname was the setup function I used on my DNS service (DynDNS)
I then turned off WiFi on my iphone.
Without changing any of my server or router settings, I could add and delete calendar events and contact entries and see them appear on my MBP plugged in to my LAN.
I could do the reverse, change stuff on the MBP and see it change on my iPhone that was using only cellular service.
I am not sure what I would do if unable to add the additional hostname to the DNS service.
Glad I could help.
One final note, verify that you have "enable hosting for this host" checkmarked in the DynDNS updater. I had lost access this morning.
The updater had listed the new server.domain.com hostname in its list, but it was not enabled. When my ISP changed my IP address, things stopped working. I clicked on the checkmark and within a minute or so, service were working again.