SMS carrier routing gateway

Design a carrier-grade SMS routing gateway (an SMPP-based messaging hub) that routes 50,000 messages/sec between application senders and dozens of mobile carriers, each carrier with its own throughput limits, encoding rules, and delivery-receipt behavior. You need least-cost/quality routing across carriers, reliable delivery-receipt correlation, and to never exceed a carrier's bind/throughput cap. How do you bind to carriers, route, and reconcile receipts?