Building an SMS-based service for users without smartphones or data

Design for the channel your users actually have:

1. SMS (one-way alerts and simple commands) - Send through an SMS gateway / aggregator with routes to Haitian carriers, or through direct carrier agreements. Check delivery rates and sender-ID support *in Haiti* specifically before committing. - Two-way SMS: users text keywords (PRI MAYI, METEO JAKMEL) to a short code or long number, and your webhook replies. Keep the command grammar forgiving (accents, case, typos). - Messages in Kreyòl, short, and without special characters when possible. Non-GSM characters (like ò, è) switch the SMS to UCS-2 encoding, which cuts the limit from 160 to 70 characters per message, and cost with it.

**2. USSD (interactive menus like *123#): works on any phone and is session-based, but requires a carrier partnership** or an aggregator. Great for menu flows (register, choose a crop, get a price).

3. IVR / voice (automated calls in Kreyòl): reaches users with low literacy.

Architecture tips: - Keep the core logic channel-agnostic (an internal API), with thin adapters for SMS, USSD, WhatsApp and web. - Opt-in and opt-out (STOP), send-time windows, and rate limits. - Budget carefully: per-message costs add up fast. Measure engagement and trim what isn't used. - Work with local organizations for onboarding. Trust drives adoption more than technology.