GDPR (General Data Protection Regulation): This is the biggest hurdle. GDPR mandates that personal data (including phone numbers) can only be processed with a lawful basis, most commonly explicit and informed consent. Using a database without this consent is a direct violation, carrying hefty fines (up to €20 million or 4% of global annual turnover, whichever is higher). https://b2bdatabase.co/product/uk-whatsapp-number-database/