think that the short message originated from circuit switched/packet switched network(legacy network) has to terminate in the same network. if there is an IP-SM-GW, does the short message have to go through the IP-SM-GW anyway?
Operators may choose to design their networks so that message all go through some nodes if they had some driver for this, but it is definitely possible to send SMS messages within a network and between SS7 networks without going through an IP to SS7 gateway, if that is your question.