Hello
I encounter a major limitation in the daily use of my Proton contacts on mobile (Android and iOS): the inability to use these contacts for making phone calls or sending SMS via my phone's native applications without manually exporting them.

Currently, to call a contact, I must:

Open the Proton Mail app.
Navigate to the Contacts menu.
Select the contact and initiate the call from the Proton interface.

This process is cumbersome and not ergonomic compared to using the native address book.

My suggestion: I would very much like to see implemented a solution enabling transparent and secure synchronization of Proton contacts to the phone's system address book, while preserving encryption.

Several technical approaches could be considered:

Dedicated "Proton Dialer/Messenger" app: A lightweight application that integrates with Android/iOS app selectors (intents) to handle calls and SMS using local decryption keys, without exposing raw data to the system.
Official CardDAV support: Enable secure CardDAV synchronization (similar to what some private providers do) where the Proton app acts as a secure bridge to inject decrypted contacts only at the moment of use into the system address book, without persistent unencrypted storage.
Advanced Widgets or Shortcuts: Intermediate solutions allowing quick access to contacts for calls/SMS without navigating deep into the Mail app menu.

Why this is important: Without this feature, many users are forced to export their contacts (as .VCF) to Google Contacts or iCloud for convenience, which completely contradicts Proton's privacy promise by exposing this data to big tech companies.

Enabling calls and SMS directly from Proton contacts, without compromising security, would be a decisive argument to convince thousands of users to migrate permanently to your ecosystem.