SMS in its classic form is justified to be expensive. It does not travel as mere data. It on the network as Intelligent Network messages which are transactional and reliably transmitted on a per-hop basis taking in each case signalling processing resource. Once it gets through the core network to the radio it once again travels on the signalling channels where the capacity is extremely limited and is at premium. It is once again reliably transmitted and the acknowledge once again goes back with hop-per-hip reliable transmit to the SMSC. If the sender has enabled message receipts, that repeats twice just for good measure. In all cases it uses signalling capacity and signalling processing which costs an arm, a leg and a prosthetic because it is originally designed to deal with voice call setup, billing, mobility, authentication - all things that need to work 100% of the time.
If you want to design the most expensive technical way to transmit a message in a mobile network that is SMS. It was designed as a "cool, see what we can do with it" and nobody had a clue how popular it will become. If the people who designed it had an idea of how popular it will be they would have never designed it that way.
Now at some point someone devised as nice scam by making it possible for handsets to use GPRS to transmit/receive SMS messages straight from the SMSC. That is a scam because it costs under 1% of what SMS costs to transmit while it is being billed the same. However, I have so far seen only one operator to enable this feature. Most just stick with good old signalling capacity for this because it gives them a technical justification to charge the premium for it. You see - it actually costs us to transmit it that much.
It is the same story as with not using divert to temporary ISDN numbers in international roaming which has been in the GSM standard for 15 years now. If it is used a call between two roaming handsets in the same country will not need to be routed back to the home country. So there will be no justification to charge an exorbitant roaming premium from dolts arranging where to get and get hammered while gunning down the piste at 40mph. However, because it is not enabled by any operator, they can happily charge crazy roaming fees for such calls and these charges make up a very tidy sum for operators in tourist countries like Austria, Spain or Greece.