When Ludacris wanted to learn what it would take to make it as a successful rapper, he did the closest thing possible to hijacking the local antenna and broadcasting his own songs 24/7 until a label appeared with a contract for him to sign: he became an on-air personality. At Atlanta’s hip-hop flagship, Hot 97, Ludacris, then known as Chris Lova Lova, made a name for himself as a gregarious kid whose eagerness to get on the airwaves made him an enthusiastic, valuable asset to the station. Within months, he went from answering phones to hosting his own nighttime program. All the while, he was scheming to get Incognegro, his independently released first album, heard.

Eventually, access to the celebrity nexus paid off. After Scarface became president of Def Jam South, he made the radio jock his first signing. It was a sage move. Back for the First Time, a reworked version of Incognegro, went on to sell more than three million copies. The follow-up, 2001’s Word of Mouf, sold more than two million.

Ludacris has become a potent, respected MC for the same reasons that he was so loved on air. He’s incredibly lucid. He’s randy, which is de rigueur for someone who has to field all manner of calls from the public. Behind a mike, either in the studio or on stage, Ludacris commands a crowd better than just about any other contemporary performer.

His only misstep thus far has been taking himself too seriously as a rapper and pursuing one of hip-hop’s great indulgences — aiming to make stars out of his crew, the Disturbing tha Peace posse, on their mediocre debut, Golden Grain (Universal). He himself is in top lyrical shape here, but no one else is. On the air as a DJ, you can relegate sidemen to where they belong; as long as the star is still breathing, the underlings never get their own show. In hip-hop, the same is rarely true.

Often pride is a curse. Take KRS-One, rap legend and keeper of the old-school guard. Since releasing the less-than-compelling book The Science of Rap in 1996, KRS has been arguing that rapping skills can be taught, transferred from the mouth of the teacher to that of the student. I presume Angie Martinez was meant to be the example that proved the rule. A drivetime host on New York’s Hot 97, perhaps the most influential urban radio station in the country, Martinez had barely fantasized about a rap career before KRS took it upon himself to turn her lyrical water into the cheapest of wines.

The teacher, in this case, seems to need a little remedial training of his own. Angie’s 2000 debut, Up Close & Personal (Elektra), was a less than compelling display of artistic talent. On air, she’s a folksy host who peppers her speech with colloquialisms ("For real, ma?") while softballing her way through the hip-hop cavalcade. Occasionally she asks the hard questions, as she did of Jay-Z after his well-below-the-belt jab at Nas last year, "Superugly." But playing the sister for all seasons has won her access to hip-hop’s finest, and she’s muscled them into album-saving guest spots: Prodigy, Wyclef Jean, Snoop Dogg, and Mary J. Blige on her debut and Missy Elliott, N.O.R.E., and Kelis on her recently released follow-up, Animal House (Elektra).

In most cases you can judge a party by the guest list, but the only thing this line-up proves is the size of the gaps that needed to be filled. Round-the-way affability works when killing time between club bangers. On the mike, it’s nothing short of a recipe for disaster.

And though the radio route to stardom has become tried and true in hip-hop, elsewhere it’s still a novel phenomenon. Witness the rise of Laura Cantrell, alterna-country chanteuse and host of one of the New York area’s most charming country-radio programs, on mega-indie WFMU. Her two albums — 2000’s Not the Tremblin’ Kind and the new When the Roses Bloom Again (both Diesel Only) — are quaint reminders of country’s inherent capacity for storytelling without resorting to the vapid pop-love clichés that characterize so much new Nashville material. Cantrell sings with a voice that’s soft and shy, but a streak of independence runs through all her material. Her albums are modest gems — indeed, they wouldn’t seem out of place on her own thrift-country-radio show.