The shadowy figure who calls himself the Boy Genius racked up an impressive run of scoops — internal AT&T (T) documents, pre-release access to nearly every BlackBerry, some big iPhone exclusives — in the four years before he sold his brand to Jay Penske’s Mail.com last April in a deal reported to be worth multiple millions.

Now that he’s been bought — and his cover blown — Jonathan Geller (his real name), 23, is being trotted out to meet the press, which is how we came to have lunch with him Wednesday and learn some of the secrets of his insider sourcing.

It started, oddly enough, even before he convinced his well-heeled parents to let him drop out of Greenwich (Conn.) High School in 10th grade, having already missed 120 out of 180 school days. He’d had a cellphone since he was 10 and started a little Web design shop at age 12. He got to know some people in the mobile phone business and a few music producers, one of whom gave Geller his moniker. Somehow (he’s a little vague about this) he started getting his hands on new-model cellphones before they were released to the public. And he started supplying them to a rarefied clientele: rap stars — P. Diddy and Ludacris are the two names I recognized — who got a kick out of having the newest thing in their pocket.

Access to products meant access to information, which by age 17 he was retailing to the gadget sites — Engadget and Endgaget Mobile. In 2006 he launched his own blog, BoyGeniusReport.com, since re-branded as BGR.com.

Our lunch in a Manhattan hotel restaurant covered a lot of territory, from Apple’s (AAPL) Steve Jobs to the imminent slide of Research in Motion (RIMM) to the weakness of Microsoft’s (MSFT) mobile OS efforts. Highlights below the fold:

• On checkbook journalism: Like any mainstream publication, BGR pays for photographs. Unlike most publishers, however, Geller has occasionally paid for news stories — most recently an e-mail exchange with Steve Jobs whose authenticity Apple disputed. See here.
• On taking pre-release cellphones: He’ll do it, and later buy a phone to replace it, but only if he can satisfy himself that he’s not getting stolen property. “If the PIN is dead, that means it’s stolen.”
• His relationship with Research in Motion: Although he claims RIMM’s share price jumped 30% after he broke a story about the BlackBerry Pearl, he is not loved by top management. “I must have at least 100 cease-and-desist letters.”
• On Apple’s security: “They’re tough. There’s nothing that’s not under their control. If there’s a leak, it’s either one of their people or their Asian manufacturers.”
• On the prototype iPhone that Gizmodo purchased: “I wouldn’t have touched it with a 10-foot pole. Two reasons: 1) You know it’s stolen. 2) It’s Apple, so you know they’re going to come after you.”
• On RIM: “Within two quarters, their market share is going to slide.”
• On Microsoft Windows Phone 7:  “It’s down to Apple and Android.”

We found Geller to be an ambitious young entrepreneur who, for someone who trades in corporate secrets, is surprisingly open about his craft. We’re a little skeptical about his plans to expand his brand, however. He, with the help of three or four other writers, has built a following of somewhere between 1 and 2 million unique readers on the strength of his contacts in the mobile phone business. Whether he can achieve the same kind of success in gaming and tech business coverage — he mentions publishing corporate earnings before they are released — is less certain. And he loses us when he talks about getting into merchandising. BGR beanies and refrigerator magnets, anyone?

[Follow Philip Elmer-DeWitt on Twitter @philiped]