While most of the focus has been on Apple and its iOS -- the mobile operating system that powers the iPhone and iPad -- Google's Android also collects location information from users' smartphones.

Yesterday, that it tracked users but said it would make changes to iOS. Later in the day, CEO Steve Jobs told the Wall Street Journal and The New York Times that his company would participate at the hearing.

Meanwhile, Google has said it collects location data from Android phones only when owners opt-in. "Any location data that is sent back to Google location servers is anonymized and is not tied or traceable to a specific user," the company told the IDG News Service on Monday.

Earlier today, a crisis communication expert for taking a week to respond to questions about iPhone location tracking, saying that the company "dropped the ball in a big way."

And because Congress had gotten involved, Apple faces a long investigation into its privacy practices, predicted Michael Robinson, a senior vice president with Levick Strategic Communications, a Washington, D.C. firm that helps companies deal with public relations emergencies.