Auto-SMS & WhatsApp Post-Call - for sell this service to bussiness owners

I need a small Android utility that silently springs into action the moment any incoming or outgoing call ends. The flow is straightforward: first it fires off a local SMS from the phone’s own SIM using... (Budget: ₹1500 - ₹12500 INR, Jobs: Android, Android App Development, Android SDK, Java, Kotlin, Mobile App Development, Mobile Development, PHP)