An SMS hub usually implies P2P messaging, and is used by mobile operators to send messages to operators they do not have reach to via SS7. The advantage of using a hub is that it reduces the number of commercial agreements a mobile operator needs to maintain, but it is not the highest quality route since the hub adds another hop in the delivery chain and may not report back actual delivery notifications. Sending A2P messages via an SMS hub is usually frowned upon and not permitted by most mobile operators.
