Short answer: Use a personal number only for founder-led, low volume. Move to WhatsApp Business (app or platform) when you need labels, quick replies, and a number the company owns. Consider API / BSP setups when volume, multi-agent, or official templates matter. Always log leads outside the chat thread.
Personal number — fine until it is not
Pros: fast, human, zero setup. Cons: holidays, lost phones, no shared history, ads pointing at a private life. Fine for week one of a solo shop.
WhatsApp Business app
Business profile, away messages, quick replies, labels. Still one device mindset unless you add a shared process. Better than personal for most SMEs starting paid traffic.
API / multi-agent paths
When several people must answer, or you need templates and audit trails, you outgrow the single-phone model. Pair any path with a sheet or CRM so ownership survives the app.
What Viewkeeper recommends
Ship the lead spine first (capture → log → owner → reminder). Then pick the WhatsApp tier that matches volume. VK Leads assumes WhatsApp stays the front door — structured behind it.