Free 411 (1-800-FREE411) has surpassed the 100 million use milestone. The relatively new service has still only captured a small percentage of the US directory assistance market, but is rapidly gaining ground. According to the company this means US callers have saved approximately $150 million (citing $1.50 for the average lookup).
The company provides its information services for free in exchange for a small advertisement that each caller hears before completing the call. While it's not a mobile play per se, a high percentage of information calls are made on the go when it's harder to lookup things.
A young New Jersey based mother was the 100 millionth caller and won an all expense paid vacation to Puerto Rico.