iHeartRadio, the Clear Channel-owned streaming music service, announced today that it reached 97 million unique listeners last month and 50 million total registered users.

IHeartRadio’s service competes with the likes of Pandora, Slacker, and other smart radio services. It offers both a directory of local terrestrial (aka traditional) stations online as well as a smart radio feature similar to what Pandora offers.

As for iHeartRadio’s growth, the service didn’t disclose how many of those 50 million registrations were active monthly listeners (so it’s hard to say how many people simply signed up and never signed back in again). Because of iHeartRadio’s close ties with major radio companies, it’s been able to run what looks like a pretty successful advertising campaign with audio ad spots on several local radio stations.

Still, the 97 million listener number for May is impressive and something that should help push people into picking up their smartphones to hear the radio rather than the AM/FM radio dial.