(CNN) -- If you're like Derek Smith, you spend a lot of time on your smartphone. Then again, maybe nobody is quite like Derek Smith.
In one recent week, the medical student sent 40 e-mails and 399 text messages, snapped 25 photos, bought two movie tickets, downloaded four songs, watched a full-length film, checked the weather forecast 15 times, shopped at Target, surfed the Web for 129 minutes and spent 5½ hours socializing with friends on Facebook -- all from his iPhone 4S.
"I am not my phone, but my phone is a reflection of me," said Smith, 26, of Louisville, Kentucky. "It does a pretty good job of taking my life and folding it up into a nice little lightweight, pocket-sized summary. It's almost like I am holding a copy of my brain in my hands."
As part of our Our Mobile Society series on how phones and tablets are changing our lives, CNN asked a handful of people to document everything they do on their smartphones over the course of a week: every text, every tweet, every minute spent scrolling through Instagram or playing "Words with Friends." Some of the results are displayed here.
It was an unscientific project. Our volunteers, self-described smartphone addicts, are probably much more active on their handsets than the average person. The idea was simply to demonstrate, whether we realize it or not, how much of our daily lives now is conducted through these little glowing screens.
It's not just that we're on our phones a lot. It's that these devices have become time capsules of our lives, documenting our work, our social interactions, our purchases, our travels, our passions and our guilty pleasures.
In one week in early September, Kathleen Baker sent 256 e-mails from her phone, many of those as part of her duties as director of housing for a university. She also posted 34 updates or comments on Facebook, "liked" 18 posts and read 93 posts from friends (55 of them on her birthday). Somehow, she also spent another nine-plus hours that week using her phone to surf the Web, play games, check her bank balances and listen to audiobooks and music.
"I actually didn't log as many hours as I thought I would," said Baker, 46, who lives with her husband and their three young children in Seattle. "I didn't include any time that I used my phone to entertain my kids. ... I am very aware of my dependency on my phone, so it wasn't too surprising.
"The phone definitely helps me keep up with all the moving parts of my life. I am almost always on the go, and it allows me to juggle everything," Baker added in an e-mail. "While some people may feel tied to their jobs because of technology, I am happy to have the advantage of owning a smartphone. I can't imagine how I would juggle a crazy job, three kids/family obligations, and doctoral studies without it! I am a happy addict."
Like Baker, most people who shared their smartphone-usage habits said they view their phone as a hugely positive thing in their lives, not a burden or the root of an unhealthy addiction.
"My friends tell me that I am easily the most accessible person they know. My phone is my lifeline, and any attempt to reduce usage is just silly," said Stephen Anfield, 31, a freelance writer and social-media consultant.
Anfield, who lives in Alexandria, Virginia, just outside Washington, sent 423 texts during the week he tracked his phone use. He also sent 228 Twitter messages, checked in to 26 locations on Foursquare, posted nine photos to Instagram and placed three orders from Five Guys Burgers.
Oh, and he received two voice mails. He still hasn't listened to them.
Like many people who participated in this experiment, Anfield prefers to communicate via text or e-mail. And like the others, he finds it difficult to go more than a few minutes without checking his Droid Razr. He sees his phone almost as an extension of himself.
"If somebody picks up my phone, it does make me nervous," he said. "It's not a privacy issue. There's nothing that I'm hiding. I just think it's a very personal item."
Smith, the Louisville med-school student, said he didn't realize just how much he used his iPhone until he documented his usage for a week.
"I was stunned by just how integrated my phone has become in my life. It is almost an anatomical appendage, attached to my person as though it were a part of my hand," he said. On the few occasions Smith has left home without taking his phone, he's become anxious and depressed.
"My palms get sweaty, my heart races, I start biting my lip," he said in an e-mail. "My mind is occupied by thoughts of going home to get the phone. I feel cut off from the world."
After jotting down all his phone usage and staring at the page -- almost 800 text messages sent and received -- Smith wondered whether he was relying on his phone too much. Should he cut back? Was he missing out on the world around him? Were his relationships suffering?
Ultimately, he decided no. Smith also uses his phone to study and do medical research, and he believes the benefits of using it outweigh any potential downside.
"We do need to be careful not to digitalize our entire existence, not to replace our lives with a microchip," he said. But Smith believes that his phone enhances, and not detracts from, his real-life human interactions. To him it breaks down barriers and gives him freedom.
"I feel like my desktop/laptop anchor me into one place. They are ancient in a sense, the electronic devices of our parents and grandparents," he said. "I do not want to be trapped by the confines of a desk and chair, and today's world is not as compatible with that type of device. Today's world is too fluid for that."