VentureWoods has a very insightful commentary by Ashish Tomar of Nokia. Here is his take on SMS:
SMS is a 15-year-old technology, and many advanced IP-based messaging technologies have been available for several years. But still, SMS heavily dominates the messaging traffic in mobile networks. I believe, operators have so far failed to exploit the messaging technologies.
In terms of functionality, SMS is a fairly limited technology. Messages can contain only plain text, up to a maximum of 140-160 single-byte characters, and session/dialogue features such as threads or buddy lists are not supported.
Lack of local-language input handsets: This means customized handsets to support local market requirements, resulting in costly handsets. As a consequence, most SMS are sent in English, confining the active text market to a small group of educated users, primarily based in the cities. Although SMS in China is a different story, thanks to Chinas economies of scale.
Relatively high pricing of SMS compared with voice tariffs.
lack of interconnect: Interconnection of SMS messages is a pre-requisite for growth.