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According to Warren, Windows Phone 8.1 is secretly supporting Apple's Passbook application. Warren added that he has been using the feature on his flights. "Works perfectly," he tweeted.
Microsoft didn't announce the said feature when Windows Phone 8.1 was officially revealed earlier this month.
iMore's Rene Ritchie has a theory, which makes sense. Ritchie said that Microsoft may be using Apple's Passbook file format to render the files on Windows Phone 8.1 through Microsoft Wallet. Ritchie noted that Apple code-signs Passbook cards, so it is still unclear how Microsoft handled Apple's certificates.
It is possible to read and render the .pkpass file. There are even Passbook apps on Android that support the feature.
Both Microsoft and Apple declined to comment on the report.
The surprising feature is still in developer preview beta, so its fate is still unknown. Microsoft may ditch the feature in the future. Or, Microsoft may be testing Apple's reaction here. There's also a possibility that both companies have an official agreement.