Three layers of numbers
Delivery says the message arrived. Engagement says someone did something: clicked, replied, entered a code. Outcome says it was worth sending: an order, a booking, a renewed subscription. The report gives you the first; the other two come from your own systems, and they are the ones to optimise.
Links you can count
Use a link on your own domain with a campaign parameter, for example ?c=sept-sale, and count visits and orders on your side. Avoid public shorteners: they are the most filtered pattern in SMS and they hide your brand. A short path on your own domain costs the same characters.
Cost per outcome
Campaign cost divided by outcomes. At a cent a message, a campaign of 50,000 costs 500; 400 orders is 1.25 per order. That figure, not the delivery rate, is what you compare with email or ads, and it is usually the reason SMS stays in the mix.
Opt-outs are a metric
An opt-out rate under half a percent per send is normal. A jump after a change of cadence or tone is the audience telling you something. Opt-outs are permanent for that list, so the cost of a careless campaign is paid on every later one.
Comparing two sends
Change one thing at a time: the hour, the first five words, the offer. Split the list randomly, not by country, because sender rules and delivery differ per destination and would drown the effect. Tag each half with a different campaign so the reports line up.
Something unclear or out of date? Write to [email protected]; corrections are folded back into the guide and the update date changes.