Whistle is a global sales development agency that specializes in building and running SDR functions for fast-growing B2B companies. Acting as either a fully outsourced SDR department or as an extension of in‑house teams, Whistle focuses on creating predictable pipeline through multi-channel outreach across phone, email, and LinkedIn. The company emphasizes performance, transparency, and close alignment with each client’s ideal customer profile, rather than just supplying headcount.
Founded in 2020 by brothers David and Yonah Zeff after multiple successful SaaS exits, Whistle has grown into a 100% remote team of more than 100 people distributed across time zones. The team spans SDRs, account managers, RevOps specialists, data researchers, and content strategists who collectively design and execute go‑to‑market programs. According to the company, its customers have raised over $2 billion in funding and generate well over $15–16 million per month in pipeline sourced from Whistle’s SDR efforts.
Whistle’s core offerings include a fully managed SDR Agency service, appointment setting and SDR staffing (“Hire SDRs”), Data on Demand for human‑verified B2B contact data, and RevOps for HubSpot as a Platinum HubSpot Partner. These services are packaged to help companies that lack an SDR function plug in a complete operation within about 10 business days, or to help more mature revenue teams scale coverage into new segments and territories. The agency is particularly focused on SaaS, technology, and other complex B2B sales cycles where multi-touch, multi-channel outreach and tight CRM integration are critical.
In the SDR and lead generation market, Whistle positions itself against traditional appointment-setting firms by combining rigorous SDR vetting (accepting roughly 0.2% of applicants), strategic consulting, and deep CRM/RevOps capabilities. With more than 300 companies served worldwide and over $100M in opportunities generated for clients, it has established a presence in the outsourced SDR landscape, especially for startups and scale-ups that need to spin up or expand pipeline generation quickly without building a large in-house SDR team.
