Short answer: send the gaming compliance notice by email, poll its delivery state on a schedule, and send SMS only when a documented timeout expires; this gives you an auditable fallback, but it cannot give you webhook-level timing because both channels are pull-driven.
The bill is made of email sends, repeated status reads, SMS fallback sends, and whatever storage you retain for evidence. For N notices, a worker capped at K email checks makes at most N x K polling reads before fallback, while an SMS fallback rate of F adds N x F sends. That makes the polling interval and timeout policy operational cost controls, not mere tuning knobs. Start with the compliance deadline and work backward; don't poll every second just because a loop makes that easy. Delivery reliability is the primary decision axis here. An email open is not a dependable substitute for delivery evidence — privacy features can hide the recipient's network address and prevent senders from seeing whether a message was opened — so the audit record should preserve provider delivery states and your own decisions rather than infer receipt from tracking pixels. A team that retains one normalized observation per transition has a different storage curve from a team that saves every unchanged poll response; neither policy changes the recipient outcome, but it changes how much evidence remains when an investigator asks why SMS was sent. Decide that before setting the cadence.
