An SMS aggregator is a wholesale intermediary that holds connections to many mobile operators and resells message delivery to gateways and large senders.
Few companies connect directly to hundreds of operators. Aggregators do, and sell that reach wholesale. A gateway may terminate traffic through one or several aggregators per destination, choosing on delivery rate, sender fidelity and price. A message to a given country can therefore pass through two or three intermediaries before the operator.
The number of hops is invisible to the sender but shows in behaviour: receipts that arrive late, sender IDs replaced somewhere along the way, or a route that degrades when one link is congested. Good gateways measure each route and swap it when it degrades.
At SMSMeteor: a destination has one active route, chosen on measured delivery rate rather than the lowest wholesale price, and changed without altering the published rate mid-campaign.