According to UNESCO, more than 95% of the world's population uses radio. That high figure probably says it all, but to put it in even more perspective, this is compared to roughly one-third of the global population having access to Internet at all (let alone reliable or high-speed connections).
As of 2010, at least 75% of households in developing countries have access to a radio, while only 20.5% of households in developing nations have access to the Internet.