Google Voice has more than 1.4 million users, and of those, 570,000, or 40 percent, use the service every day, according to a confidential part of a letter Google sent to the FCC, which was disclosed by BusinessWeek. Additionally, according to the letter, Google may expand the service internationally. The figures on the growth and popularity of the service give some greater context to a fierce debate over the service between Google and AT&T.

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