In yet another blow to Apple’s iAd mobile advertising platform, the group is losing iAd boss Andy Miller, All Things Digital reports.

Miller, who co-founded mobile ad company Quattro Wireless, which Apple bought for $275 million in 2010, is leaving Apple to become a general partner at Boston-based Highland Capital. His departure is yet another sign that Apple is struggling to morph into an advertising company. It was recently reported that Apple has lowered its iAd prices and reduced restrictions to keep clients from jumping to rivals.

We’ve pinged Apple for comment on the report and will update when we hear back.

Apple announced its plans to jump into mobile ads with iAd in June 2010, and it subsequently closed down Quattro’s ad network last summer. The company pitched iAd as a way to deliver media rich ads on native iOS apps, but its reach is limited, since the ads only appear on Apple devices and have no way of extending beyond apps. Competing ad networks like Greystripe let advertisers run campaigns across multiple mobile platforms and mobile websites, not just apps. Apple certainly didn’t help its case by demanding tight control over ads initially (a policy it has since relaxed).

The company has its work cut out for it. Unlike Google, Apple doesn’t have much experience as an advertising company. At times, Apple has seemed downright hostile to the very concept of ads. As tech journalist Dan Frommer points out, Apple CEO Steve Jobs recently cheered the fact that Apple’s new iCloud email wouldn’t have any ads: “No ads,” Jobs said. ”We build products that we want for ourselves, too, and we just don’t want ads.”

At the moment, iAd seems like a distraction for Apple. But the company will likely keep trucking along, since mobile advertising is such a huge market. The Wall Street Journal recently reported that mobile advertising grew 79 percent in 2010 to reach $743.1 million, compared to just $416 million in 2009.

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