This is what to tell a customer that wants the Telecom X phonebook on their phone or computer. The same three address books appear in every client; only the Personal book can be edited, and edits made on the device are written straight back to the phonebook.

Clients that support discovery can be given just the host name or the e-mail domain - /.well-known/carddav redirects them to the right place.

1. Settings → Apps → Contacts → Contacts Accounts → Add Account → Other.
2. Add CardDAV Account.
3. Server: api.telecomx.dk, User Name: the e-mail address, Password: the password, Description: e.g. Telecom X.
4. Next. The three address books are fetched immediately.

iOS subscribes to Apple push on its own, so changes made elsewhere show up within seconds without the phone polling.

1. Contacts → Settings → Accounts → + → Other Contacts Account.
2. Account Type: CardDAV, Server Address: api.telecomx.dk (or the full URL above).
3. User Name and Password as above.

Android has no built-in CardDAV client. Use DAVx5 from Google Play:

1. + → Login with URL and user name.
2. Base URL: https://api.telecomx.dk/carddav/, user name and password as above.
3. Select the address books to sync and let DAVx5 create the account.

DAVx5 polls on the interval it is configured with - Apple push does not apply.

Thunderbird, eM Client, Evolution and similar are given the same base URL. Anything that speaks CardDAV over Basic authentication works; the server serves vCard 3.0.

• The books are named in the employees own language - Personlig / Fælles / Kollegaer in Danish, Personal / Shared / Colleagues in English.
• Only Personal accepts changes. Adding or editing a contact in Shared or Colleagues is refused by the server with 403, and the client will show a sync error.
• A contact deleted on the device is deleted from the phonebook - it is a real two-way sync, not a copy.
• Contact pictures are fetched from the image server through a URL that carries the employees own token. Removing the account and adding it again mints a fresh token, so old pictures may need a re-sync.
• If the password is changed, the client keeps sending the old one until it is corrected. Repeated failures register as brute force attempts and can get the whole location blocked, so fix or remove the account rather than leaving it failing.