Acting as 'gateway' to other content.

The number of ringtones downloaded in the U.S. has quadrupled in the last year, according to a new report issued by research firm Ipsos-Insight. Additionally, ringtones seem to be acting as a "gateway" application of sorts, leading users to experiment with other types of mobile entertainment content.

Ipsos' TEMPO quarterly study of digital music behavior found that 23% of U.S. wireless subscribers have downloaded a ringtone, compared to 5% reported for the same period last year.

As expected, younger subscribers are the heaviest downloaders, as more than half of the 12-to-24-year-old wireless subscribers have bought a ringtone, at 52%. Wireless subscribers aged 25-30 come in second at 30%, 35-54 next at 17%, and 55 and older users last at 5%.