Whistle

Whistle is a global Sales Development Agency founded in 2020 by brothers David and Yonah Zeff, following three tech exits. The firm connects growing companies with vetted SDR talent to accelerate pipeline generation, either through fully outsourced SDR teams or by embedding sales development professionals within clients' in-house sales organisations. It operates entirely remotely, with a team of more than 100 sales professionals averaging over five years of experience.

The company works across two service lines. Its fully outsourced SDR department delivers qualified meetings for clients and generates more than $15M in client pipeline per month. Separately, Whistle places elite vetted SDRs who integrate directly with in-house sales teams. Hiring is deliberately stringent: only one in 500 SDR applicants is taken on, placing successful candidates in the top 0.2% of applicants. Emphasis is placed on delivering qualified meetings rather than activity alone.

Whistle serves SaaS, technology, startup and enterprise software businesses. It has worked with more than 300 companies, whose customers have raised over $2Bn in funding, and has generated more than $100 million in opportunities for its clients. Documented case studies report returns of 13X and 89X.