Hangouts, Google’s texting and internet-based calling app, is a lot more capable with CallKit in tow. When a call comes in, Hangouts can answer from iOS’s call UI (user interface) and display it on the iPhone’s lock screen. Hangouts can ring any person from iOS’s contact list, and can even interface with Siri — calling someone with a voice command rings them via Hangouts.
It is comparable to Facebook Messenger’s CallKit implementation. In Messenger, incoming calls take up the full screen and show the caller’s name and call controls. Answering a call pulls up Messenger, which you can dismiss, and maximize resume, like the native iOS phone app. And it works in CarPlay, Apple’s dashboard-optimized interface — you can answer call using Messenger while driving.
To enable CallKit integration in Hangouts, install the newest app from the iTunes App Store. Then launch it, tap Settings, and toggle Answer on lock screen.
CallKit is capable of more than just voice-call integration. It can transcribe voicemail messages and serve up callback buttons alongside visual voicemail notifications, and a specialized set of APIs lets Hangouts and other apps tie into iOS’s favorites, recents, and lockscreen features.
And that is just the tip of CallKit’s iceberg. A second component, Call Directory, enables call-screening services to cross-reference a pre-defined list of known spammers when calls come in. With an app like Truecaller installed, for example, phone calls from unfamiliar contacts display information from the Truecaller database — including whether the number is from a known fraudster.
