Carriers let out a harmonious groan when Apple unveiled its new iMessage service last year. Not only was it a texting alternative, but it would automatically switch users over from texting to iMessaging if both parties were on iOS 5 devices.

Unsurprisingly, this has had a significant impact on the wireless industry and its subsequent text messaging business. According to a new report, the amount of text messages sent during Q3 this year declined for the first time ever…

Fierce Mobile (via 9to5Mac) reports:

“U.S. mobile operators raked in third quarter 2012 data revenues of $19.9 billion, up 3 percent quarter-over-quarter and 17 percent year-over-year–despite suffering their first-ever decline in overall text messaging traffic and revenues, according to new research from Chetan Sharma Consulting.

Although U.S. subscribers still send an average of more than 650 text messages per month, data indicates that messaging revenues have peaked, Sharma said. “It might be early to say if the decline has begun or the market segment will sputter along before the decline takes place.”

We certainly saw the decline in text messaging coming. During Apple’s iPad mini event last month, Tim Cook announced that iOS users sent more than 300 billion iMessages in its first 12 months at a rate of nearly 28,000 per second.

And iMessage isn’t the only texting alternative out there. There’s Google Voice and Kik. WhatsApp announced last year that it was delivering more than a billion messages a day. And don’t forget about social networks like Twitter and Facebook.

The good news for carriers is that as one pay-for service declines, another rises. Wireless providers brought in $19.9 billion in data revenues last quarter, up 3% quarter-over-quarter and 17% yoy. And with more and more devices getting built-in cellular radios, we don’t expect this growth to stop anytime soon.

How do you text? Do you send carrier text messages, or do you use iMessage or some other service?