Miller first came to Apple after --mobile advertising firm Quattro Wireless--in 2010. Quattro was subsequently dissolved in favor of Apple's iAd service, which Miller served as the vice president and general spokesperson for. The soon-to-be-former VP will head to Highland Capital, notable as the Boston-based venture firm that originally helped fund Quattro.

Though it's unclear exactly why Miller chose to leave (Apple did not respond to s request for comment), it's possible that he experienced dissatisfaction with the iAd program, which has had its ups and downs in the year or so since its launch in 2010.

Billed as an innovative (and interactive) take on mobile advertising for Apple's iOS platform, with several prominent sponsors--including Disney, Nissan, and General Electric--committing more than $60 million in advertising dollars to the service.

In subsequent months, iAd faced initial challenges: U.S. regulators looked into whether the service ; Apple's led the company to open advertising up to , and offer software for creating iAds called ; and some advertisers saw and experienced general dissatisfaction with iAd in contrast to other mobile advertising platforms.

Despite its initial growing pains, however, iAd expanded into both and in subsequent months. And in December of 2010, an that iAd held 21 percent of mobile advertising revenue--not the lion's share of revenue, certainly, but nothing to sneeze at either.