Research firm Gartner says that SMS continues to increase in usage, however the increasing prevalence of IM clients on phones is shifting that balance.

Some 2.3 trillion messages will be sent worldwide during this year, a 19.6 percent increase over the year previous. However, at the same time revenues have leveled off due to increased competition.

"In many markets, there has been strong pressure on operator margins for text messaging services and this has been driven by often intense competition between carriers," research director Nick Ingelbrecht said.

The US and Canada still lags behind the rest of the world, making up only 189 billion of those texts. That should increase to 301 billion this year, Gartner said. About two SMS messages are sent each day by mobile phone users, close to the global average of 2.1 per day.

The world's most prolific texters reside in Southeast Asia, where mobile phone penetration is extremely high. The Philippines lead the way with 15 per day, followed by Singapore with 12.

But explosive growth in SMS is about to end, Gartner argues. With the growth in IM and social networking on the phone, it is becoming unnecessary to use texting to communicate.

Gartner argued that IM should become a mass-market application for the phone akin to the way it has for mobile e-mail in developed market.

"To sustain growth over the next few years, carriers should look to social-networking applications to drive traffic, working where possible with popular established social-networking sites," Ingelbrecht suggested.