There’s a subtle, but potentially hugely important, change happening in cell phone use in the U.S.: For 2009 figures, the amount of digital data sent over cell phone networks surpasses voice traffic for the first time. The future has arrived.

The New York Times has a piece about this, quoting Dan Hesse–Sprint’s CEO–on the matter: “Originally talking was the only cellphone application … But now it’s less than half of the traffic on mobile networks.” This is supported by data from CTIA, an industry body, that shows the average number of voice minutes per U.S. user has fallen for the last two years, and that the average time taken for local calls was just 1.81 minutes in 2009, versus 2.27 in 2008. If you think about it, this is probably also borne out by your own experience–it certainly is in my case, and I’ve recently switched to a pay-as-you-go solution for calls, as it’s more economic.

The U.S. has finally caught up with the SMS trend, many years after it exploded across Europe, and CTIA data shows that the number of text messages sent by the average U.S. user leaped 50% in 2009 from the previous year. But it’s really in terms of mobile data consumption for video, Net surfing, in-app use, email and so on, that the big switch-over has happened. And remember that by far the greater number of phones still in use on these networks aren’t the data-munching smartphones like iPhones or Android devices–they’re the old-style dumbphones, which may be capable of limited Net browsing and picture messaging, but which still serve the primary task of phone calling and SMSing.

This means that the minority devices on the grid (the smartphones) are consuming the majority of over the air traffic: More than anything else, this is a demonstration that the future is arriving early.

Yet, despite the transformational impact of new touchscreen smartphones, with the iPhone in particular leading the charge in changing the industry, some people still don’t get it. NPD analyst Ross Rubin is quoted in the NYT as thinking smartphone handset designs have “become far less cheek-friendly,” which is simple hogwash for those of us who remember the early days of cell phone design. And even the C seems to agree with Rubin’s assertion that modern touchscreen and qwerty-keypad phones aren’t as good as simple dialpad dumbphone interfaces for “quickly dialing a phone number,” with touchscreens often requiring a “swipe through several screens” before dialing is possible. Both these facts are misleading, as qwerty-keypads typically include built-in numeric dial pads, and on many smartphones it takes but a heartbeat to press to dial a contact.

Nevertheless, soon, particularly when next-gen 4G networks start to take off properly, cell phone use will be almost exclusively about data consumption, and voice calls will remain as a needed but deprecated service. And when that happens, something odd will happen to the cellphone providers themselves–they’ll be relegated to merely being vanilla pipes over which your lovely smartphone data flows. This is why they’re scrambling to establish some mindshare at the moment, with weird efforts like Verizon‘s own App Store.