Built the first SMS-based marketing system at PECFEST: opt-in updates funded by sponsors, marketing tagline at the tail. The OGs.
The setup was simple. We collected phone numbers at registration with explicit opt-in. The system pushed schedule updates and event reminders to the list. Sponsors funded the messaging in exchange for a short tagline at the tail. Send-side cost stayed low because every message did two jobs.
By 2009, every Indian bank, telco, and pizza chain was doing the same thing.