For years wireless carriers in the U.S. have been making a good chunk of revenue from text messaging, charging anything from around 20 cents a text to $20 a month for an unlimited texting plan. But growth in the volume of text messaging is slowing down as smartphones with access to messaging apps and email continue to rise.

According to the wireless trade organization, 'only' 1 trillion texts were sent in the second half of 2010. And while that still represents an 8.7% increase from the prior six months, it's also the slimmest gain in the past decade.

The trend will likely to continue with services like BlackBerry's Messenger and the yet to be launched iMessage from Apple. Interestingly, the Wall Street Journal says that Google is also working on its own instant messaging service for Android -- though they already have Google Talk. Whatever the case, AT&T believes that high demand for texting plans will persist for a long time because they are not locked down to a single platform.

Instant messaging apps from WhatsApp to Kik let people exchange text and photos across different platforms without being charged extra, but the fact remains that a vast majority of people are still using so-called feature phones where these apps aren't available. That's going to change over time as smartphone adoption continues to grow, and we're not only going to see a decline in SMS usage but also in regular voice calls as people start using VoIP.

Unfortunately, some carriers will likely charge customers more for data use to make up for the decline.

In my case I haven't had the need to pay for a texting plan in a while since $30-40 plans already come with an unlimited SMS allowance where I live, and even so I still rely more on WhatsApp -- or BlackBerry Messenger before I switched phones. I'm guessing this will vary significantly from countries and carriers. Are you still paying for SMS?