I think you meant to end that with "phone calls" rather than "to deliver SMS?" SS7 was used for that, but had a significant amount of idle time since most phone calls are much longer than the time needed to setup the connection.
I do indeed mean SMS, but I was focusing more on the air interface. There, SMS definitely consume resources in the same way that calls do (although of course at a very different rate: SDCCH uses 0.8 kbit/s, as opposed to 13 kbps for full rate voice/CSD traffic channels).
