Online SMS verification in the central anti-spam database.
Possibilities:
- Blacklist / Whitelist
- Blocking not of the digital senders, blocking of all senders who are not on your contact list.
- SMS blocker
- Antispam, spam blocker

Do not worry about the confidentiality of your information. Only “fingerprints" (SHA-256) of your SMS from senders who are not in your contact list are sent to the Internet.