Analysts have estimated that iMessage, which is built into every iPhone, iPad and Mac, has as many as 1 billion users globally, but Apple has not disclosed any figures for several years. Apple and Microsoft have argued with Brussels that some of their services are insufficiently popular to be designated as “gatekeepers” under new landmark EU legislation designed to curb the power of Big Tech. Brussels’ battle with the two US companies over Apple’s iMessage chat app and Microsoft’s Bing search engine comes ahead of Wednesday’s publication of the first list of services to be regulated by the Digital Markets...