Apple is once again slashing the minimum amount marketers must spend to roll out campaigns across its iAd mobile advertising network, AdAge reports.

Advertisers must now commit $100,000 to launch an iAd campaign, down from the previous minimum of $500,000. (Some sources cite $400,000 as the most recent minimum.) When Apple first unveiled iAd in 2010, the company demanded a minimum $1 million campaign investment. AdAge notes Apple also will tweak its billing formula: In the past, the company charged a fixed rate for every 1,000 iAd impressions and tacked on an additional fee every time a user clicked on the promotion. Apple will now bill only the cost-per-thousand rate.

Another significant change: Apple will award iOS app developers 70 percent of iAd revenues, up from the previous 60 percent. AdAge explains the move is intended to compensate for lower ad rates and to incentivize developers to build their businesses on iOS, which is the second largest smartphone operating system in the U.S. according to recent comScore data. Google's Android dominates the U.S. market at 47.3 percent, followed by iOS at 29.6 percent.

The new pricing model follows weeks after Apple hired former Adobe executive Todd Teresi to lead the iAd effort. Teresi replaced former vice president of mobile advertising Andy Miller, who bolted Apple's ranks in mid-2011 to join venture firm Highland Capital; Miller previously co-founded Quattro Wireless, which Apple purchased in early 2010 for $275 million. The Quattro platform made up the foundation of the iAd initiative.

As of late 2010, iAd ran neck-and-neck with Google's AdMob for control of the mobile display ad market, but as 2011 wound down, Apple slipped to third overall, falling behind Google at 24 percent and independent mobile ad network Millennial Media (17 percent) to grab 15 percent of the market, according to research firm IDC. Insiders say ad agencies are frustrated by Apple's high prices, inflexible contract options and demands for creative control, not to mention rich media formats optimized solely for iOS devices--by comparison, AdMob and Millennial Media campaigns run across multiple operating systems.

AdAge adds that while Apple declined to comment on the report, the company has already begun communicating details of the iAd changes to advertisers and developers.