At Verizon’s developer conference today, the largest U.S. carrier unveiled details of its new application store that will launch in the fourth quarter and potentially disrupt what has been a $1 billion business for the carrier.

The most important piece of information revealed so far in the morning session was that Verizon (NYSE: VZ) will follow Apple’s lead, by sharing 70 percent of revenues with developers and by keeping 30 percent for themselves. Developers who choose to use the V CAST Apps store will also have access to the carrier’s billing platform, other APIs, such as a user’s location and marketing via Verizon’s web site, which is the No. 26 web property in the U.S. and has 60 million registered users (half of which visit the site every month).

Verizon also announced a partnership with Research In Motion, which has rolled out a separate BlackBerry App World for its phones. RIM’s Jim Balsillie said it will pre-load the VCast App store on to the device, but that won’t prevent users from downloading the App World to the device on their own. John Stratton, Verizon’s EVP and CMO: “Why in the world does the industry need another app store?...Our desire is to complement those environments by lending resources and tools for app developers and customers.”

VCast vs. App World: Stratton said that if developers today are already in the BlackBerry App World, they are going to make it “a straightforward process” to getting into the VCast store. “If you have developed for the App World already, you are good to go.” He said the reason why developers would also want to submit it to Verizon is so they can get access to additional merchandising, direct carrier billing, and other APIs. If you don’t want that stuff, then that’s OK, too. “This has got to be a frictionless point here.”

Advertising Campaigns: Developers wanted to know if Verizon would support their apps through ads, like Apple (NSDQ: AAPL) is doing with their “There’s an app for that” campaign. Stratton: “I would tell you yes. We are pretty aggressive advertisers. We’ve raised up the profile of apps in meaningful way.“riverfs of market share.

Free Apps: Balsillie and Stratton both had opinions about free apps. Stratton said another announcement in regards to its Brew platform is coming later today that will allow developers to make a free app and monetize it however they like—that’s something new. (See a related link on Verizon’s expanded partnership with Qualcomm’s Brew platform.)But Stratton cautioned, “We need to be careful though. We need to improve the status quo or conventions around how to merchandise so the premium apps that you develop don’t get lost in noise, or limitless supply of free apps.” Balsillie: “I’m not a big fan of a mile wide and an inch deep. I’m into stickiness. I think titillation is phase one of this stuff, but it’s about richer substance. Rather than downloading 30-40 apps you use once and never use again, I think the benchmark of success will be stickiness.”

• Verizon Wireless Looking To Woo RIM and Windows Application Developers
• Updated: Verizon Wireless Confirms App Store Coming By Year-End; Is Qualcomm Involved?