One of the big reasons for the rise in mobile phone usage is that you can call anywhere in the country for the same price that you can call your next-door neighbor. This lack of long distance charges has led to many people getting mobile phones who ordinarily may not have been interested. Also, many people now use their mobile phones exclusively, after canceling their home phone service. Having one less bill to pay is definitely a positive.
According to the CTIA, a wireless trade association, more than 270 million people in the United States own a mobile phone, so this is a trend that may eventually do away with land lines altogether.