CardDAV

CardDAV is a shared address book. SipWarp and your cell phone both talk to one server. You save a contact here, and after the phone refreshes, the name is on the phone too. You add someone on the phone, press Test in SipWarp, and the name shows up here. One list, two devices, no CSV in the middle.

That is the reason to use it. Import and export still work. CardDAV is how the list stays the same without you remembering to copy a file.

Fill in Settings, CardDAV

• URL is the server, starting with https://. A host is enough if the server advertises its address book. Example: https://contacts.example.com.
• Username and password are the login for that server, not your SIP password.
• Press Test. SipWarp downloads the book. The status line tells you whether it found the address book.

After Test works, Save on a contact uploads that person. The iPhone does not update at that instant. Open Contacts on the phone and pull to refresh, or wait for its next sync.

If you do not have a server yet

You do not need to rent one.

• Radicale is a small free CardDAV server. It runs on a Raspberry Pi or any computer you leave on. SipWarp and the iPhone both use https:// and that computer's address. This is the straightforward home setup.
• Nextcloud already includes contacts. If you have a Nextcloud account, the CardDAV address is usually https://your-server/remote.php/dav. Use your Nextcloud username and an app password if the host asks for one.
• Fastmail and some other mail hosts include CardDAV with the mailbox. Their help page shows the exact URL. Paste that into URL.

iCloud can share contacts too, but it wants an app-specific password and a longer URL. Radicale or Nextcloud is the easier start.

The server has to be reachable from both this PC and the phone. A book that only exists on a PC the phone cannot see will not sync.