I have an original 1st generation Apple Watch Sport paired to an iPhone 6.
While at home, I had a scenario where my iPhone's battery died while I was typing out a text message. Without thinking, I held down the Digital Crown to send my message using Siri.
To my surprise, a few moments later I felt my Apple Watch ringing with a phone call from my friend.
Somehow, I was able to send texts and answer phone calls on my Apple Watch, despite my paired iPhone having a dead battery.
How is this possible?
Best Answer
This is WiFi calling and iMessage in action.
iMessage is a messaging service that is brokered through Apple's iCloud servers and delivers point to point messages to multiple devices instead of needing SMS to deliver a message to a mobile phone. This allows messages on macOS, iPad, iPod touch and Apple Watch to send and receive messages "from" and "to" mobile numbers.
WiFi calling is even better - it links the carrier directly to your Apple devices that are not your iPhone. It is basically a VOIP bridge from the iCloud authenticated devices to a gateway server that bridges the call to the telephone network.
Pretty amazing time to be alive — our phone calls, video conferences and messages are now bits to be sent and received as digital data streams.