The celebrity Web site TMZ.com posted two photographs and a video showing Shriver holding a phone to her ear while she was behind the wheel. That prompted Gov. Arnold Schwarzenegger to write about it on Twitter, where he said "there's going to be swift action."
Shriver says she will donate her favorite old cell phone to a program that helps domestic violence shelters.
She added: "That's my version of swift action with a higher purpose."
Shriver's statement did not say whether she would use a hands-free device in the future. Her office had no further comment.