Liza Colburn uses her cell phone constantly. She taps out her grocery lists, records voice memos, listens to music at the gym, tracks her caloric intake and posts frequent updates to her Twitter and Facebook accounts.

The one thing she doesn't use her cell phone for? Making calls.

“;I probably only talk to someone verbally on it once a week,”; said Colburn, a 40-year-old marketing consultant in Canton, Mass., who has an iPhone.

For many, cell phones have become irreplaceable tools to manage their lives and stay connected to the outside world, their families and networks of friends online. But increasingly, by several measures, that doesn't mean talking very much on them.

For example, although almost 90 percent of households in the United States now have a cell phone, the growth in voice minutes used by consumers has stagnated, according to government and industry data. This is true even though more households each year are disconnecting their landlines in favor of cell phones.

Instead of talking on their cell phones, people are making use of all the extras that iPhones, Androids, BlackBerrys and other smartphones were also designed to do — browsing the Web, listening to music through Pandora, watching television, playing games, and sending e-mails and text messages.

The number of text messages sent per user increased by nearly 50 percent last year, according to the CTIA, a group that tracks the wireless industry. And for the first time in the United States, the amount of data in text, e-mail messages, streaming video, music and other services on mobile devices in 2009 surpassed the amount of voice data in cell phone calls, industry executives and analysts say.

“;Originally, talking was the only cell phone application,”; said Dan Hesse, chief executive of Sprint Nextel. “;But now it's less than half of the traffic on mobile networks.”;

Of course, talking on the cell phone isn't disappearing entirely. “;Anytime something is sensitive or is something I don't want to be forwarded, I pick up the phone rather than put it into a Tweet or a text,”; said Kristen Kulinowski, a 41-year-old chemistry teacher in Houston. And calling is cheaper than ever, due to fierce competition between rival wireless networks.

But in the last few years, industry data shows, the growth in the average number of voice minutes per user has steadily slowed, to 3 percent in 2009, from 75 percent in 2000 — and that average, experts say, could be skewed by a subset of heavy talkers.

Even the telephone design industry has taken note. Ross Rubin, a telecommunications analyst with the NPD Group, said cell phones outfitted with numerical keyboards — easiest for quickly dialing a phone number — were no longer in vogue. Touchscreens, or quick messaging devices with full qwerty keyboards, on the other hand, are. On the newest phones, users have to press several buttons or swipe through several screens to get to the application that allows them to make calls.

“;Handset design has become far less cheek-friendly,”; Rubin said.

Hesse of Sprint said he expected that within the next couple of years, cell phone users would be charged by the data they used, not by their voice minutes, a prediction echoed by other industry executives.

When people do talk on their phones, their conversations are shorter; the average length of a local call was 1.81 minutes in 2009, compared with 2.27 minutes in 2008, according to CTIA. For some, the unused voice minutes mount up.

“;I have thousands of rollover minutes,”; said Zach Frechette, 28, editor of Good magazine in Los Angeles, Calif., who explained that he only dialed when he needed to get in touch with someone instantly, and limited those calls to 30 seconds. “;I downgraded to the lowest available minute plan, which I'm not even getting close to using.”;

Frechette said part of the reason he rarely talked on his phone was that he had an iPhone, with its notoriously spotty phone reception. But also, he said, most of his day was spent swapping short messages through services like Gmail, Facebook and Twitter. That way, he said, “;you can respond when it's convenient, rather than impose your schedule on someone else.”;

Others say talking on the phone is intrusive and time-consuming, or seem to have no patience for talking to just one person at a time. They prefer to spend their phone time moving seamlessly between several conversations, catching up on the latest news and updates by text and on Facebook with multiple friends, instead of just one or two.

“;Even though in theory, it might take longer to send a text than pick up the phone, it seems less disruptive than a call,”; said Jefferson Adams, a 44-year-old freelance writer living in San Francisco. By texting, he explained, “;you can multitask between two or three conversations at once.”;

Nicole Wahl, a 35-year-old communications manager at the University of Toronto in Canada, estimates she talks on her phone only about 10 minutes a month.

“;The only reason I ever call someone anymore is if I don't have their Twitter handle or e-mail address,”; Wahl said. “;Like my hairdresser to see if she has a last-minute appointment or my parents to say I'm dropping by.”;

American teenagers have been ahead of the curve for a while, turning their cell phones into texting machines; more than half of them send around 1,500 text messages each month, according to a recent study by the Pew Research Center's Internet and American Life Project.

Colburn, from Massachusetts, said she caved to the pleading of her 12-year-old daughter Abigail for a cell phone to send text messages with her friends after she and her husband discovered it was hindering her from developing bonds with her classmates.

“;We realized she was being excluded from party invitations and being in-the-know with her peers,”; she said.

Colburn said texting had also become a much easier way to stay in touch with her daughter and receive quick updates about after-school plans.

“;The other night she texted me from upstairs to ask a vocabulary question,”; she said with a laugh. “;But I drew the line there. I went upstairs to answer it.”;