Everything worth knowing, nothing that isn't.
How SMS routing works
For each message the platform looks up the destination's home operator (after any number portability), consults the routes available to that operator, and picks one by your policy — cheapest, highest quality, or a blend. The message is submitted over that route's SMPP or SS7 interconnect, and the delivery receipt confirms the outcome. An HLR lookup first ensures the number is live and correctly attributed. See /operators/smsc-gateway and /answers/hlr-mnp-number-intelligence.
What least-cost routing (LCR) actually does
LCR maintains a rate table of every route to every destination and, per message, chooses the lowest-priced route that satisfies quality and regulatory constraints — then fails over to the next if it degrades. Pure lowest-price routing is a trap: the cheapest path is often a grey route, so mature LCR weights price against measured deliverability and sender-ID support, not price alone. See /answers/what-is-lcr and /answers/what-is-route-failover.
Direct routes vs grey routes
A direct route terminates over the destination operator's official A2P agreement — reliable delivery, sender-ID support, and traceable receipts, at a higher wholesale price. A grey route sneaks A2P in as cheap P2P through SIM boxes or foreign HLR backdoors; it is cheaper but delivery oscillates, sender IDs break, and operators block it. Least effective cost, not lowest sticker price, is the right metric. See /answers/what-is-grey-route-sms and /answers/what-is-grey-route-sms.
Benefits of quality-aware routing
Lower effective cost per delivered message once re-sends and failures are counted, higher and more stable delivery rates, preserved sender-ID branding, and clean operator-specific delivery receipts for troubleshooting. Automatic failover keeps traffic flowing when a route degrades, and direct routing keeps you compliant with operator and regulator rules. See /answers/what-is-dlr and /answers/what-is-throughput-sla.
Limitations and what to watch
Rate and quality tables must be kept current or LCR optimises against stale data; over-indexing on price alone routes you onto grey paths whose apparent savings evaporate in failed messages and broken sender IDs; and route quality shifts as operators block and aggregators re-route, so continuous DLR monitoring is essential. The signal to watch is oscillating DLR success on a suspiciously cheap route. See /answers/what-is-hop-by-hop-latency and /platforms/esme-cdr.
Is the cheapest SMS route always the best?
No — the cheapest sticker price is frequently a grey route whose real cost is higher once undelivered messages, re-sends, and broken sender-ID branding are counted. The right metric is least effective cost: the price per successfully delivered, correctly branded message. BroadNet routes on direct operator agreements across 1,000+ operator connections — direct to the operator in 86 countries, reaching 200+ — so cost is optimised without sacrificing deliverability. See /operators/smsc-gateway and /answers/what-is-grey-route-sms.