A new IDC Research report, sponsored by Facebook, looks at the various ways in which people are using their mobile devices during a typical week.

The study, which looked at the mobile habits of nearly 7,500 18-44-year-olds over the course of one week in March, found that just under half (49.4%) of the U.S. population is using smartphones – about 155.1 million people. And that Facebook is used by 70% of them. That’s #3 overall, just behind web browsing at 73% and email and 78%. Facebook usage beat out games, maps, photos, and video streaming.

Since the study was paid for by Facebook, there’s plenty of data on how Facebook is used on mobile devices in a typical week. First off, Facebook was found to account for 1 in ever 4 minutes spent on social and communication activities on smartphones. The average survey participant spent 32 minutes and 51 seconds on Facebook every day. Out of the 70% of people that use Facebook on their device, 61% said that they check it every day.

That roughly 33 minutes spent on Facebook every day breaks down like this: 16 minutes browsing the news feed, nearly 10 messaging, and just over 6 posting statuses and photos.

These Facebook sessions last, on average, about 2 minutes and 22 seconds and people check Facebook around 14 times a day, on average.

The study also looks at other aspect of mobile use apart from Facebook, and some fo the findings are interesting:

• 25% of those surveyed said that they can’t even recall the last time their smartphone wasn’t next to them. Another 24% said that they spend less that 30 minutes throughout the day without their device within ear shot.
• 34% said they feel “excited” when they post a photo on Instagram, and 27% feel excited while posting LinkedIn updates.
• Half of those surveyed said they tell Facebook when they go to the movies. 13% tweet about it.
• 79% of people reach for their smartphones within 15 minutes of waking up. 62% do so immediately after waking up. Those numbers only increase when you narrow it down to 18-24-year-olds.
• People are only using 16% of their communication time on their phones to make calls. All the other time is spent texting, emailing, and social networking.

For the complete study, head here. It’s a pretty interesting look at the current state of mobile connections in the U.S., if you can deal with a little bit of obvious bias toward making Facebook look like the all-consuming timelord. Come to think about it, who’s really going to argue with that notion?