Providing your phone number is optional in OpusChat. However, it may be useful to provide your number under the following circumstances:
    - To allow OpusChat to auto-add friends from your phone book. See how to auto-add friends.
    - To add your phone number to your OpusChat account for account recovery purposes. See how to add phone number to account.
    - To recover your OpusChat account using your phone number. See how to recover account by phone number.