The Voice Agent Margin Curve: Why Call Handling Becomes Agency Infrastructure in 2026

Voice agents stop being a novelty when 83% of B2C marketers already run AI agents, which makes phone coverage a baseline expectation rather than a differentiator. The agency economics flip because a retainer built on measured call volume, escalation accuracy, and remaining labor can be priced from real samples instead of seat counts. Agencies that ignore the category keep selling hours into a channel where the client can now measure every missed call.