In-app purchases are a significant portion of Apple App Store revenue on iPhones, Gartner said, without giving an exact amount.
"Users are not put off by the fact that they have already paid for an app and are willing to spend more if they are happy with the experience," Blau said.
In fact, the growth of in-app purchasing will pose a challenge for developers, Gartner said. "Users only pay when they are happy with the experience and developers have to work hard to earn the revenue through good design and performance," Blau said.
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