A growing number of Americans are using mobile phones to keep up with or play a role in politics, but some say they are getting unwanted political messages, a study showed Tuesday.

The Pew Internet & American Life study showed some voters are using smartphones as real-time fact-checkers or to post political messages to social networks.

The report found 88 percent of registered voters own a cell phone of some kind as of September, and 27 percent of the phone owners used the devices to keep up with campaign news or political issues in general.

Nearly one in five have sent text messages related to the campaign to friends, family members, or others and five percent have signed up to receive text messages directly from a candidate or other group.

But five percent said that they have received unwanted election-related text messages that they did not sign up to receive.

Forty-eight percent of the voters surveyed said they have a smartphone, and within the group, 45 percent have used the device to read comments on a social networking site about a candidate or the campaign, and 35 percent have checked the truth of campaign statements, the study found.

Among smartphone-owning voters, 18 percent have used the device to post comments on social networks about a candidate or the campaign, the survey showed.

Mobile apps are playing a relatively minor role in the campaign, according to the Pew report. It found 45 percent of cell-owning registered voters use apps, but just eight percent of them use apps from a candidate, political party, or interest group.

The survey conducted September 20-23 interviewed a sample of 1,005 adults including 872 cell phone owners, 731 of whom are registered voters.