Apple (AAPL) Faces EU Warning to Open Up iPhone Operating System BloombergEU antitrust regulators tell Apple how to comply with tech rules ReutersEU compels Apple to improve iOS interoperability with third-party smartwatches, headphones and other accessories 9to5MacEU to Offer Apple Guidance on Digital Rules Compliance The Wall Street JournalEU warns Apple it must open its iPhone operating system to rival developers MarketWatch