NPD's just-released "Mobile Phone Usage" report found that 45% of U.S. mobile users use their phones just for calls, and only 20% for "all-in-one multimedia," which includes a wide range of activities ranging from music listening, video viewing, Web surfing and picture-taking to text messaging, mobile gaming, adding ringtones, and Bluetooth connectivity.

The majority of mobile phone users are aware of text messaging and the ability to change ringtones, NPD said, but on the other hand, 34% don't know if their phone has expandable memory, 28% don't know if they can watch videos, 23% don't know if they have GPS, 21% don't know if they can play music, and 12% don't know if they have Wi-Fi Internet access.

The research firm pointed out that according to its own monthly Mobile Phone Track service, 71% of all handsets purchased in the U.S. can play video, 60% have expandable memory, and 55% have GPS technology.

"Operators and other handset retailers have an opportunity to educate consumers as to the capabilities of their handsets in the wake of slower overall handset sales," said Ross Rubin, director of industry analysis for NPD, in a statement.

The results of NPD's Mobile Phone Usage Report came from an August online survey of 4,681 pre-identified mobile phone owners ages 13 and older.