A new survey from the Pew Internet and American Life Project shows that 19%, or nearly 1 in 5, of Americans who use the Internet also use Twitter or some other type of social networking “status update” service.

Although these results are being widely touted as showing how widespread Twitter use is, that’s not necessarily true. Because the question included not only Twitter but also other status update services–such as Facebook–it’s impossible to tell how much of this activity is really on Twitter, as opposed to other social media sites.

The survey also reinforces just how important mobile phones have become for social networking. Only 10% of people who have only one Internet-connected device (such as a computer) report using status updating services, but nearly 40% of people who have 4 or more Internet-connected devices use these social media services.

The survey also shows that more than half (55%) of those who use status update services are under age 50.