An affiliate commission is the share of a referred customer's spending paid to the person who referred them; in SMS gateways it is usually a percentage of top-ups for a fixed period, tracked by a link or a code.
Gateways grow through people who recommend them: developers, comparison writers, community members. A referral programme pays them a percentage of what referred accounts deposit, for a period, with attribution through a link that sets a cookie or a code typed at sign-up. Good programmes pay in the same way the product is paid, show counts and amounts without exposing who the referred customers are, and forbid self-referral, spam and brand bidding.
At SMSMeteor: 10% of top-ups for 12 months, 90 days attribution, paid weekly, in the coin you choose. Terms on the affiliate page.