Everything worth knowing, nothing that isn't.
Keep messages to one segment
Every message over 160 GSM-7 characters is billed as two or more segments. Trim copy, drop the emoji that forces Unicode (which cuts the limit to 70), and use a URL shortener for links. See /answers/what-is-concatenated-sms and the /tools/sms-segment-calculator.
Validate numbers before you send
An HLR lookup tells you whether a number is live, which country and operator it is on, and whether it has been ported — so you drop invalid numbers and route correctly instead of paying for undeliverable sends. See /products/hlr-lookup and /answers/what-is-hlr-lookup.
Fix the route, not just the rate
Grey routes advertise a low unit price but fail intermittently, forcing re-sends that erase the saving. Direct routes cost more per message and less per delivered message. See /answers/what-is-grey-route-sms.
Register sender IDs and classify correctly
Unregistered or mis-classified sender IDs get dropped by operator firewalls — you pay for messages that never arrive. Register once, classify transactional vs promotional correctly, and stop leaking spend. See /answers/how-to-register-sender-id.
Match the channel to the message
For conversational or media-rich flows, WhatsApp or RCS can beat stringing together many SMS segments. Run the two-way traffic where it is cheapest and keep SMS for universal-reach alerts. See /products/omnichannel.