Almost all Android apps can do this in realtime, because to get the IMEI/device ID (a questionable thing in itself), Google decided you should also be required

Almost all Android apps can do this in realtime, because to get the IMEI/device ID (a questionable thing in itself), Google decided you should also be required to have permissions to see who is calling/called. It's a major privacy violation, with Google directly encouraging it for no good reason. (Getting device ID should be a very rare, high-security permission; instead each app should get a unique app+deviceID. And seeing who is calling is likewise a rare thing that should be highly suspect. Or Google could add controls or do on-demand like MS and Apple do...)